I've heard of using buttercream, pudding/custard, creme diplomat, creme chantilly... cutting them in half and using a scoop of ice cream.
Honestly, since the pastry is pretty much unsweetened, it's more or less a delivery system for whatever sweet confection we decide to put in there. Now, that being said, I don't know if I'd do the buttercream again -- I think it was too stiff so, when I bit into it, it took a little bit to get the flavor of the cream with the texture of the pastry onto the palette.
I think that using one of the other cremes, something with a little looser consistency, would definitely make it a better tasting experience.
Thanks for the comment, though -- I wouldn't have pondered that otherwise, really.