Hmmm
For a composite stock, one made from a laminated composite/epoxy resin material.
Place a piece of drawing paper over the stock and draw the shape you want the riser to be. Take that off, cut it out and trace on cardboard. Cut that out and you have a good template. Trace that onto your stock.
Use thick masking tape and layer by layer, build up the outline of the cheek r riser to form a dam in the thickness you want the riser to be off the stock.
Cut out carbon or fiberglass cloth using the cardboard template from earlier.
Now, take a drill or dremel and put crap loads of holes or better , divots in the cheekrest area to give resin something to tooth into. Better to not puncture thru laminate, but 1/2 way thru is good.
Lay in your cloth/resin up to top of tape and then cover and force air out with some stretchy saran wrap.
Leave it for a couple days in a room 20degrees C to 30C. Then peel off saran and let it cure another day.
Sand smooth and detail. Fill any anomalies with 2 part epoxy putty.
Paint as desired.
Sounds complicated but it's dead simple.
Most guys seem so afraid to modify their mcmillans and other higher end stocks.... It's not difficult if you are at all handy, to make mods to stocks to adapt them to your personal needs.