Hi Erik,
the short answer is yes, you can, because there are aerosol mold release sprays that have vaseline in them. But there's a caveat to it.
The first thing is that if you do decide to use vaseline, let the silicone soak it all up (and it will believe me). If you don't, your cast piece will be covered in a film of vaseline that you will have to thoroughly scrub off with dish soap before you can prime and paint your piece.
The second thing is that, should you not let it soak up you may end up with brush strokes on your cast in places where you unevenly applied the vaseline.
The aerosolized mold releases apply a more even coat. If you then also want a matte finish, I suggest lightly dusting your mold with cornstarch (don't use baby powder, some ingredients can react with the resin) and shaking off the excess. It aids in releasing your cast, adds another protective layer to minimize the chemical stress on the silicone jacket (nothing you can do about the heat I'm afraid) and, as stated before, gives your cast a lovely matte sheen.
This also results in the primer or paint sticking to the cast a lot better than if it had a polished finish.
I hope that helps, if you have more questions don't hesitate to ask!
Lisa
