You can stabilize the cream with gelatin; for 1c. cream, dissolve 1/2 tsp. gelatine in 1Tb. water in a small cup(5 min.); whip all but 2 Tb. of the cream to soft peaks. Put the gelatin in a pan of hot water until it melts; stir in remaining 2 Tb. of cream and add to partially whipped cream; finish whipping. This will hold at least 24 hrs. (refrigerated, of course).
If you were holding straight whipped cream, this is good advice, but the pudding is stable enough to hold everything together. After a couple days, gravity will do its thing, but it should be fine for a while.
The premise was that it wouldn't hold, and your first answer assumed the same; without trying it, I'm inclined to agree- you need the cream to hold it's own structure.
I've made lightened pastry cream in the morning for use later in the day. Ideally, you would make the pudding, chill....and then fold in the whipped cream last minute, but depending on the application, you could probably assemble it a few hours in advance.
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