Look for a xylene based, or at least a high xylene content, adhesive for best results. Trick is to wash silicone rubber surface with a bit of xylene to help "activate" it, then apply your xylene based adhesive to high impact poly. Then join. Should be solid. Xylene based, or high xylene content are not hard to find - ellsworth should be able to recommend a few. Good luck.
I have bonded similar kind of substrates successfully with a primer called "770" and Cyno adhesive called "401" . This are products from Henkel Loctite. An engineering adhesive company.
