Use shortswords, call them rapiers, say they look like rapiers, they are still mechanically shortswords.
Or get your DM to add rapiers to shadow hand weapon lists, why they can't be on both shadow hand and diamond mind lists I do not know.
ILM; Why wouldn't he go grey elf? He wants to play a dex and int based character, and grey elves add to both those stats while not penalizing anything important to him.
I have no idea why people are advocating rogue 7. Why? He wants to be a duelist, not a rogue. Swash gets him full sneak attack progression, fighter bonus feats, full BAB, and d10 HD. He's going to need the feats to set up melee combos, like knockdown+imp. trip or robilar's+dual hit+high sword low axe with an aptitude rapier to sub in for the axe. Hell, with a pair of aptitude rapiers he could even use Lightning Mace. 12-20 crit range and Lightning Mace isn't half bad.
Golem Strike, Plant Strike, and Grave Strike are all 1st level swift action spells. You can get wands of them, and the FAQ clarified that swift action spells cast from wands still only take a swift action to use. You can also get a greater truedeath crystal, or a demolition crystal. Sadly, nothing will let you sneak attack oozes (I can think of a dozen ways in which to use a weapon more effectively against a jellylike creature... start with /slicing bits off/ instead of /stabbing/, but I guess that doesn't count) but oh well, can't have anything. When you're up against something you're not ready for/aren't prepared for... smoke bomb, ninja vanish! Or whip out your bag of explosive runes, toss it, blow a kiss in your enemy's general direction, and detonate it.
Swash base doesn't make the strongest duelist... you can make better just with full swordsage and using maneuvers like greater insightful strike etc. You can also do it better with a gish, psionic, arcane, or divine base. But swashbucklers make the most /duelisty/ duelists. Rogue 7 isn't even better than swash 8+stacking feats, and it's less duelisty.
One thing you might want to look at/ask your GM about is changing the level 2 swordsage ability to key off int instead of wis - dex+int+light armour to AC has some obvious synergies for a duelist. I'd also ask if you can use the Unarmed Swordsage variant, because being able to punch people is a duelisty thing as well.
If you're supposed to be the 'rogue' of the group, you'll likely need to invest in search and (sigh) maybe even disable device, if your group/GM is hostile to alternate methods of trap removal like using summoned monsters or adamantine light picks. Elf is nice for that because you don't have to be constantly searching for secret doors allatime. You've got good enough stats to have a high cha, so you'll have to decide if you want to up your social skills. Pick up at least tumble, jump, and balance, regardless, as as a duelist you'll get use out of those. Where possible challenge people to duels. Preferably in the middle of combat, cause that's just fun.