[Haskell-cafe] Extensible static checking of dimensions?

The very nice Buckwalter and Denney dimensional-numbers packages both work on a fixed set of base dimensions. This is a significant restriction for me--I want to avoid adding apples to oranges as well as avoiding adding meters to grams. Is it possible to have an extensible set of base dimensions? If so, how usable can such a system be made? Is it very much worse than a system with a fixed set of base dimensions? thanks, -m