Not really I think, the context pointer (I would call it "user data" though since that's more common in the C world) is normally passed around as an opaque poin

Not really I think, the context pointer (I would call it "user data" though since that's more common in the C world) is normally passed around as an opaque pointer which is used by the allocator functions to find their own state, but not for passing additional parameters to the allocator.