you may want to try framing it with the glass restin on the actual artwork... if the glass was ever removed, i'm not sure how much of the crayon and oil pastel would stick, so if you put it under glass in this fashion it owuld probabally not be possible to remove it and retain the exact same amount of waxy medium on your board....it would also be hard to hold the glass over the piece without chance of smearing it while you set it in the frame...
Another idea would be to decide if there are parts of the painting that are more one kind of pastel than others (i'm not sure how much you've mixed the media).... It would then be possible to mask off the oil pastel and the crayon (a very low tack tape shouldn't stick to the oil pastel or the crayon if you dont push too hard), and spray a fixative onto the dry pastel. The oil and the crayon may still be subject to smearing (i've found oil pastel wont smear very easily after the oil has almost completely soaked into the paper, anyway), but the pastel wont fall off.
you could also even varnish the oil and the crayon... but the problem here would be that a water based varnish would tend to disolve the crayon, and an oil based varnish would disolve the oil pastel....
I can understand how you would be perplexed
just spraying the whole thing with fixative might work... but the oil pastels would be more prone to running than the crayon.
I would just try alot of diffrent things on scraps of board and come to a happy medium between no fixative and smearing it into a big mess.
(disclaimer at 12 o'clock...)
Remember to experiment... i havent tried any of these techniques (i usually don't mix water and oil-soluable media), but i have alot of familiarity with both oil and dry pastels.... so i'm not liable if you turn it into a study of oil on water.
I hope I could be of some help... if you're good with a scanner, I wouldn't mind seeing how it turns out when your finished.