A quick and dirty idea I cooked up the other day. The BloodBowl Skaven are notorious for the tiny lead [pb] slots to go in the slotta base. Ordinarily I would have used matchsticks to fill the gaps either side but I didn't really have any to hand so cast my eye around the various pieces of junk I have acquired from the wife's hobby supplies to re-purpose for my own hobby activities and the weapon of choice this time - fun craft foam.
Cut a 2 or 3mm strip and then cut it into little chunks. Add some PVA to the slot and prod the little bits of foam in with a tooth pick or other pointy device. Eventually the PVA will dry and you will be able to cover the gap with your usual basing materials without fear that the sand will droop into the slot and look all weird.
The great advantage to this material is that even if you cut the foam too large ultimately you can squash it into the gap and the foam will conform to the hole making a nice snug fit. It's amazing the things you learn through necessity!
Not the best example but as a group the 'glowing eyes' of the Skaven do look alright, at least I'm happy with them and the much needed splash of colour lifts the figure just a little bit. Nearly finished now.