Id say do what gary suggests.. If you dont have any drills and taps small enough for a grub screw, get some high grade loctite, and loctite the pulley onto the shaft... I did this for the gears in 360's first stage disc drive and it worked fine... thats putting much more tourque through the pulley then you will be able to generate... It just makes removing the pulley a pain.

I wouldnt suggest mounting it of the rear of the motor if you can help it- its asking a lot of the bearings in the front plate of the motor over that sort of distance.

As for the ti- try it... the term grade 5 is pretty open.... put it in a vice, try bend it over with a hammer, if it cracks, try heating it ... you will need to get it cherry red until the point that the surface of the titanium looks like its gone flakey before you will be able to bend it easy.... Wear some welding gogles if you've got some while heating it.