Plum preserving/storage method that tastes like plums, not prunes (I just picked 30 lbs)
I think freezing would be your best bet - not fantastic for the texture, but when defrosted you could make a pie/cobbler or other cooked item with them. Plenty of web sites (eg http://www.fruitexpert.co.uk/using-up-a-plum-glut.html) say you can just halve them and freeze them on open tray, then when they're frozen move them into plastic bags. It's the lowest-effort option so probably worth trying on at least a fraction of your harvest.