Someone posted about this gentleman on one of the Facebook boards today but I cant find the post now to respond.
James appears to have been born in 1885 in Biggar and as has previously been discovered he was with his Pillans grandmother in 1891 and 1901. In 1911 he is listed as James Nickleson Pillans and living with his wife in Wiltshire.
There is a 1907 Attestation record for a James Pillans born around 1885 in Biggar. He joined the Cameron Highlanders. He was discharged in 1910 following conviction in a civil court for stealing a bicycle. He gives next of kin details as Father John Pillans 10 Freer street, Edinburgh, Mother Helen Pillans, brothers Thomas and John and sister Elizabeth. I had a look at 10 Freer Street in the Valuation Rolls of the period and there is no John Pillans, but there is a John Nicholson listed at that address. I suspect James was illegitimate ( born to one of grandmother Elizabeth Pillans daughters) and his father was John Nicholson ( hence the Nickleson middle name in 1911).