I think it would be a lot of work.
The new clanrats are pretty static, in rank friendly poses.
I have some of the plastic plague monks and those would be real tough to convert for BB.
But the plastic Rat Ogres would work really well.
Now if you can get ahold of a nightrunner box or the old Mordheim warband, those will be easier.
You can create linerats and gutters easily. And if you have some armor bits, the blitzers are covered.
I honestly quite like the
GW BB Skaven team. It fits what you need pretty close.
The price is high, but you can always get them online.
Either from
GW or here.
http://www.bbfigs.com/
Maybe you can get Warstore or Maelstrom to order them and give a discount?
Automatically Appended Next Post:
Just looking at
GW's site.
The team you get for $49.50 really only needs a gutter runner added.
If you check
GW, click the "View entire army product list" to find the individual player links.
They run about 8.25 each.
The Rat Ogre Headsplitter is $22.