Java moss loves being splashed out of water. If you but some on a piece of wood/stone just out of the water - but being regularly splashed (so kept moist) and with good light it will readily attach to the wood.
Set up a small waterfall in your greenhouse in summer - and it will go mad.
If thats not possible, just give it good light. Java moss is one of the toughest plants going - i've never used any CO2 or fertilizer and it certainly does very well indeed. It grows in different forms depending on conditions, but all seem hardy. Low light levels don't bother it at all - but it will grow quicker with some brightness