I think it depends on you boat as to the proportions of the tradtional "riding sail" which is a phantom storm mizzen.

If you were going to do it, you might try to simply find a used "tiny" jib and rig some lines so you could fly it along the backstay in reverse.

You might even "borrow" a tiny sail.

Then, if you find it works, have one made for you.

I think you want to find one that works -- but is NO bigger than necessary. Some boats just don't seem to respond much.

I wouldn't be adding a lot of windage at the stern, if it were me.