Well, as I understand it, in NSW, Church Records are just that, Church Records. They are not automatically Public Records. I see nothing wrong in today's custodians of Church Records expecting to collect funds for the upkeep and preservation of their organisation's private records. I see nothing wrong in today's custodians of Official Records expecting to collect funds for the upkeep of their records either ..... so NSW BDM collects fees/charges for providing copy of their historic BDM records, NSW State Records collects fees/charges for providing copy of their archival records .... Family History Groups of volunteers have fees and charges for the services they provide in searching their archival materials ....
I don't see the impossibility of a fee being remitted from the U.K. You could of course undertake to make a donation in the UK to your local Uniting Church if you are concerned about exchange rates. 
OK I've taken several deep breaths after reading this reply because to say I was insensed by it would be an understatement.
Just because someone says they hope that there wouldn't be a charge for checking already known information, does not mean that individual expects everything for free and wouldn't dream of paying out for things.
Sorry JM, but considering there are no money orders available for purchase in the UK to send to Australia and its not possible to easily obtain a cheque drawn in a foreign currency (it may in fact not be possible anyway) on a UK bank other than possibly at considerable cost, I shall not be pursuing confirming the missing blanks on that certificate on what is a distant sideline. If it had been a direct ancestor, I would have not thought twice about doing that, but if the descendants of the individuals concerned appear to have not bothered trying to confirm the detaiils (and nothing on their tree suggests they have even though the live in Australia), I really do not see why I should should have to pay out further to confirm what is a sideline and therefore doesn't affect my own directline research. I already have purchased from NSW several copy certificates and certificate transcripts on this particular line and I'm afraid I have no intention of spending any more of limited funds when that money would be better spent confirming my own directline research.
And yes I suppose I could provide a donation to a UK based United Reform Church, but that is something that my grandparents did for many years as both were elders in their local church. However, I suspect that the URC in Australia if they expected a donation, would prefer it was given to them and not a local church in the UK.
While I appreciate that unlike in the UK, Trove provides free access to your historic newspapers, and some other records are available for free on Archives websites, the vast majority of Australian records are far more expensive to obtain copies of, even with what is currently a favourable exchange rate, than their UK equivalents and it doesn't help that so many Australian organisations have not yet bothered to provide online facilities for payment. If they did, then those of us overseas may make more use of their services looking at sidelines.
I may at some point follow Sue's suggestion of following Emma Birch's siblings to see if any confirmation can be found without requiring any excessive expenditure. But after 17 years of research and a fairly substantial amount of expenditure (which I was and still am happy to do as I enjoy the hobby), my priorities still remain in researching my own directline brickwalls and not spending an inderterminate amount on sidelines overseas. While I am happy to spend some and enjoy following them forward, it is not, and I shouldn't be criticised for saying so, a priority. Considering people who descend from such lines appear to be reluctant to spend money in their own country researching these and other lines, its not up to me to confirm these things. While I would like to, I shall leave them with a "maybe" comment.
Thanks to all for your help but I think I shall leave it there.
