Pretty sure you can't mod them. I savescummed and rolled back to right after the blob got in the fort to try it since when it originally occurred to me it was already way too late, walling 'em in while your military keeps 'em distracted and stuck in place with a kamikaze attack works pretty good under certain conditions. You've pretty much gotta have the only access to the fort be behind lockable doors, otherwise the activity around wall construction and dwarves being dwarves just means they're baiting the monster right past your construction site. Helps if the monster's attacks kinda suck too of course.
Urist McSwordsdwarf: There is nothing I cannot cleave!
One Steel Sword and a water blob later...
Urist McSwordsdwarf has been struck down.
And that is why I'm sticking to 40d until the bug fixes for 2010 are out.
I dunno man, when was the last version that didn't have stuff you really didn't want your dwarves going out and fighting? Unkillable, building-destroying, trap-avoiding, AND flying is pretty brutal and seriously limits how much you can explore the new underground without everyone dying (never mind intangible like the fog monsters oh god I didn't even know there were fog monsters before reading it here), but it doesn't make things any worse than the older version where you didn't have anything to explore in the first place. Until you get a Titan like that, I guess, then you're fucked.
One thing that's pretty annoying I gotta admit, is how if there's any entry point to your fort at all they start at the edge of your map and make a beeline right for it. Goblins and stuff are pretty fun because they have to wander around exploring and go where they can see to go, you can play around with them and do all kinds of stuff, some giant frog thing that effortlessly navigates your elaborate trap maze or whatever and kicks down your front door pretty much just sucks.