I just had some of these to do for a retailer to sell on. Obviously the 20 for a tenner job lots from ebay, though. the brief was "do something special but cheap" (which means quick).
resisting the hot melt glue, and the atg gun, we made up wee "boxes" out of 6x12mm PAR about 1/2" smaller all rount than the papyrus, (you could use foamcore I guess) and attached it to the back of the papyrus using the tape as mentioned above by john, then PVA glued the PAR box onto a black mountboard.
strictly speaking i suppose planed all round wood isn't very "conservation" but in this case it was just on a mass produced papyrus for a trade job. the a simple job to make up a frame with a 15mm slip, cutting the slip and frame at the same time in the morso, and the thing looks like its floating in space.
instant attention grabber - specially with the interesting edges.
The shop we made them for is over the moon, instead of getting £25 framed for them, as previously, he's getting £50.
we've done these in the past with a cold cathode light in them- an absolutely stunning effect, but departing a bit far from conservation

Just make the spacer 30mm, use a mount to hide the light behind but leave plenty of room to see the edges of the papyrus, and the cold cathode tube gets zip-tied through holes in the backing board. You can add this lot for about a fiver, and another ten minutes work. I hasten to add, I wouldn't advocate this sort of thing for anything valuable, but its a bit of nice light relief (geddit) and can bring some fun back into your day.
If the customers see one, they want one. But its a difficult thing to sell without a demonstrator.
You have to supply it with a
separate mains adaptor for the low voltage to comply with electrical regulations, of course.
im just off to ebay right now to get some more cold cathode lights for something similar to jazz up our window display.