Pears and chocolate are a known successful combination. I'd work with that, and do a chocolate pear extravaganza. If you must have jelly, make a jelly using the pear juice.
Use chocolate to flavour a custard perhaps - or make custard and flavour half with cocoa and leave half plain (can you use vanilla beans? If you can, do).
You've said you can make your own cake, so I'd do that and soak in a little whisky and pear juice. Then layer pear halves around the edges of your trifle bowl with the cored out sides facing out. Fill centre with custard, then a layer of choc, then crumbled cake, then another layer of custard and choc. Top with grated chocolate.
Voila - chocolate pear trifle surprise