Plane Sailing
Astral Admin - Mwahahaha!
sumi said:The problem is that the party he is with is not very good at fighting -anything.
I like to think that they have a kick-ass sorceress though

It seems to me that the best thing would be to get a damage enhancement on the rapier. flaming/shocking/frost are the cheapest, but you'll always find some things that are immune. If there is a common enemy Bane is most excellent, but (and I forget exactly what your alignment is) holy is probably the most generally useful one. Most enemies are evil and doing 1d6+1+2d6 damage on all your attacks is very useful.
The other option is to get a flaming burst or something, since the rapier has a decent threat range it is more likely to come off - however it is less cost effective, on average, than just having two different energy types eg shocking+flaming. Although the rules don't support flaming+flaming (for example) I'd happily support you in trying to persuade Guido that it is a reasonable option (call it "intense flaming" or whatever, as a +2 enhancement) since mechanically it is the same as mixing two element types (+2d6 damage) but isn't as stupid a concept as a weapon which could be both flaming and frost

Cheers