If you start with green(fresh cut) osage it bends real easy and has little memory to return to. If it is a well aged stick of wood using dry heat can be dangerous. I agree with the other posters, USE STEAM! You can boil the section to be bent also.
I've bent alot of osage over the years and steam/boiling is the most reliable. Take the time to make a good bending form, don't take short cuts on bending wood for that is what starts the trouble. I know how wanting a bow done NOW can make a fella hasty and all, but slow down, be patient and set things up carefully.
Tips:
1. Make a good bending form with a reliable way to clap down the bent wood.
2. Clamp or tie on a strap of some sort that tightens as you bend the wood, it helps hold down fibers that want to seperate from the wood.
3. Thin the wood as much as you can yet still leave extra to remove cracks and problems later.
4. Make some sort of steam tube or boil in a deep bottom pot. I use a boiling pot on the wood burning stove. In the past I used a large pan with boiling water and laid the section to be bent right over the boiling pan witha lid on top of it. A large pan can heat about 6-8 inches of wood good enough to bend. Watch it closely for it boils dry fast and will burn down the house if unattended.
5. Leave it clamped for at least 12 hours.
Good luck.