He is precious! So cute!
Have you thought about making little wooden "trays" and wire hay holders to attach to the side of the cage?
If not ... you might think about getting some wire and make wire hay holders to attach to the side of the cage or to the floor of the cage. If these are mounted about the same height as her head, she could easily walk up to them and eat the hay without needing to have hands to hold it. Lava stones could be placed in these also.
Little wood trays (with a rim all the way around the top of it), could be attached to the side of the cage to place pellets in {or hay that has been cut about 1/4 inch pieces} ... placing the tray about the height of her shoulders. The rim around the top of the tray can be made of quarter round or half round molding made of pine.
You could make a series of leaping ledges that you can attach to the side of the cage in an upside down "V" formation so that he can go up and down hopping from one to another, without much trouble. {Make sure you space them like steps and very close together ... up one side and down the other.}
How about making him some PVC 'tunnels' he can crawl through from one level to another or from one place to another? PVC pipe that is 4 or 5 inches in diameter is great for this. {It's also easy to clean. }
Chinchillas tend to adapt to any birth defects they may have ... we just have to help them by making their cage handicap friendly.
Jo Ann
ADDED: Ramps of wood with Popsicle sticks or 1/2" molding attached to the surface will give him a better "grip" as he goes up the ramp. Use tiny wood screws instead of glue.