Cant you just enlarge them via front lighting the paper negative, instead of backlit like a piece of film? ie: Like you would if taking a photo of the paper neg, same thing, or scanning it etc.
Front lighting would be limited very much by the reflectivity of the paper... likely not good at all. I expect that the exposures would be ridiculously long. If you really wanted to do a reflection-based exposure, you might consider metallizing the silver in the paper and relying on the reflection from that.
One other thing you might be able to do is take infrared film, remove the AH layer, lay it on the metallized paper, and expose the holy crap out of it from the backside of the film with an IR-rich source. Especially if the print is metallized, then the halation back into the film might give something.
Something I say
[The good thing about nutty experiments is that even if the results suck, they suck in a new and original way!]
Waxing a paper neg definitely permits almost ordinary exposures... even substantial enlargements. This has been reported various times here before.