In the past I’ve completely off-the-cuffed a doomed critter NPC and focused on the descriptions and dialog to keep the fighting more personal and dramatic–it’s usually pretty easy because you have an established relationship with the critter, and the players don’t care as long as everything seems in order and they’re having fun.

That won’t quite do the trick if your critter is known as a total badass and shouldn’t be pushed over without taking a bite out of the PCs, but you can always cheat in favour of the players without hurting the game.

When I am under pressure I use Monster Forge (uses Excel). It will quick advance a creature and can use several different statblock styles. It can be found here:
http://www.nzcomputers.net/heroforge/default35.asp

I have been experimenting with 4e monster roles and minions in my 3.5 campaign. I will prolly adapt the concept of Solo monsters to my 3.5 campaign. My players loved the minion rules last session. It challenged them and gave everyone something to smack around during combat. Since I have 7 players this is very hard to do with 3.5 encounter construction rules.