I think the options (assuming a MagC) are as follows (feel free to chip in if I have left out any):-
1. Mag4C cut-down to extended 3C
2. Mag3C with stock tail-cap plus Aw's extender
3. Mag3C modified tail-cap (trimmed by Mirage Man/RCatR)
4. Mag3C with replacement tail-cap (FM wide tail-cap and, I think, Modamag's tail-switch may work as well)
5. FM's own extended Mag3C (see his sales thread)
Nos. (2) and (4) will likely result in mismatched colours. No (3) is an ingenious solution at the expense of a few threads and perhaps, a slight gap. No (1) is prob the most logical if you don't already have a Mag3C. As for No (5), if you don't already have an FM creation, you don't know what you're missing