I'd give the limbs a really good rub, until they're nice & warm before stringing it to a very low brace. 2" max. Then excersise the limbs 100 or so times by just drawing it to around 6" If there's no drama there, try a 6" brace & exersise gradually to 20" max. Brace at it's normal height & excersise again until you're at full draw (again, 100 pulls or so)
You'll need to re-train the wood into being a bow, not just a stick, almost like tillering. I went through all this with a 80 year old English Longbow & it shoots fine! Dread to think what'd have happenned if I'd just tried to brace & shoot it!