I don't see how it is abusable to have multiple energy type outputs.
After all they are reducing efficiency by adding more wires.
Not a modder, but I guess you could implement it like this (no need for buttons):
- Generator fills internal storage
- If EU-compatible wiring (e.g. Glass Fibre Cable, Superconductor) is found, output at specified rate from storage as EU
- Else if BC power-compatible wiring (e.g. Stone Conductive Pipe, Redstone Energy Conduit) is found, output at specified rate from storage as BC MJ.
- Else if UE power-compatible wiring is found, output at specified rate from storage as UE MJ.
- Else, slack.
As I said, I'm no modder, and I have only the faintest clue of how coding works, so I'm not sure if this will cause lag or other problems.
Oh and then, you'll also need BuildCraft, Ampz/Voltz/Ohmz/Wattz/Joulez/Coloumbz/Faradz/BazicComponentz and TE-compatible recipes.