Good news: You can do this!
Bad news: You have to learn how to modify the SFZ files that control the mappings.
Good news: It's not that hard to do so.
Bad news: It was probably limited to that range because it sounded pretty bad when transposed out of that range.
Good news: Maybe you can get some fashionably freakish sounds that way!
Bad news: Not all of the public likes fashionably freakish sounds.
Good news: Part of the public does.
Generally, I extend notes below "where they're supposed to go," for example with guitar expansion packs I often go all the way down to B to complement 5-string basses.