Before you even start thinking about a work rest, get or rig a better platen!!
This! The stock platen will make you say bad words.

It's made of soft, thin sheetmetal, unlikely to be flat/true out-of-the-box, and I guarantee it will get dished-out very quickly.
I used a "Pyroceram" tempered glass platen liner from USAKnifemaker on mine. I scuffed up the paint on the stock piece, and simply slapped the glass on there with JB Weld. Held it in place with rubber bands until I was confident the JB weld was cured and never looked back. The tempered glass starts out
flat and stays that way a long, long time. I profiled and beveled hundreds of blades on it, only stopping twice to pull the whole platen assembly off and lap the glass to make sure it was still pretty flat. (knifemaker flat... probably not trained-machinist flat

)
I can't help much with the work-rest issues... I took mine off almost at once and promptly lost it... I just prefer grinding freehand and having the entire platen surface available.
If you do want to use a workrest against the platen, I suspect the other posters are right... mounting it securely will be the main issue. But if you just need to get your grinds "in the ballpark" and clean them up freehand or by hand (drawfiling, etc), you should be OK.