The item I listed is a heat cure silicone
Like plastacine in sheets 10/12mm thick
You can mould how much you want,up vertical faces, do varying thicknesses
VERY versatile

I have done this a few times.
I would use a self adhesive sheet wax to simulate your part thickness in the mould, then simply pour cast the silicone into your mould. Make sure you vac degas the silicone to remove the air bubbles.
Don't spill any silicone on your mould as it may stick depending on your release system.

Look on the vac innovations site
Look under "rubber products
You will see silicon60
Cures at 80,can be used as a mould or as a pressure enhancer on your 1st cook then 're used
LOTS  of uses an ways to use,ask for a sample and have a play you will be suprised

A while back I posted about a helicopter tail boom, about 800mm long, tapered from 40mm to 30mm. Put that project on hold for a while while i did the canopy, coming back to it now. Decided i wamy yo go with 2 peice female aluminum mold and prepreg. Vacuum bagging would work but one of you guys mentioned a positive silicone plug for squeezing the prepreg to the wall. Really like the idea of it and I might be doing a run of 100 or so. The silicone plug sounds like it would really cut down on lay up time rather than bagging each one. I've done some searching and can't find much detailed info on this method. Here's some questions I have:
1- what type of silicone do I purchase for this?
2- how do you cure the silicone? I'm picturing the stuff in tubes that obviously doesn't cure inside the tube,  so I assume it wouldn't be any different sealed inside a mold. Is heat used? Is this some kind of different silicone than what I'm picturing? 
3-  what size offset does the plug need? Prepreg layup will be about 1mm. Is it absolutely necessary to make a separate smaller mold for the plug, or is there another way around that? Was thinking maybe if silicone could be cured with heat inside the actual mold for prepreg, it would possibly shrink down enough when cooling to allow layup thickness. Any other way other than separate mold? Maybe just layup one prepreg part with vacuum bag and then pour silicone inside that? 
4- does the silicone plug need to be 100% contained to be effective? If the ends of mold are left open, is the silicone just gonna expand out the ends and not put enough pressure on walls? If that's the case, I can make bolt on caps for ends of mold to contain it. 
That's all that comes to mind for now. Any advice is very much appreciated. Thanks