Thanks folks.
Bald Eagle - Heating the limbs sounds drastic. It's probably
not but I'm not sure the club would be too happy about me trying that. I can see the sense in it, but I might have to give that a miss.
TJ - I
may try the shoving method, though as you said it may affect the life of the limb I think I will probably leave it be and just save for my own bow a bit quicker.
Whitehart - I hadn't considered the possibility of a bent riser. There are a couple more the same length in the club so I'll see if any of them are better. If so I may have a game of swap-the-bow-parts and build something straight out of the available bits. No sign of the string coming off at full draw (well, it's not, at least) but I'll ask someone to take a look tomorrow and see how it is.
Thanks again.