While I'm on the subject of ballasting, you can't pour ballast onto the average layout for too long before you realise you're getting a shoe full of the stuff - closer inspection reveals it's running down the wiring holes like sand through an hour-glass. The solution, obviously, is to stop up the holes somehow, and there's a variety of ways to do this. My preferred option is to break off little beads of expanded polystyrene from spare pieces of packing material and wedge them down the holes with the tip of a screwdriver. As long as you take care not to attack the wire with the screwdriver this is a quick and simple solution - the polystyrene will easily mould itself to fill the hole around the wire.
I make no claim that this is an original idea, I'm sure hundreds of people already use the technique. The reason I labour this point, however, is that earlier in the week someone forwarded a newsgroup post to me where a contributor was trying to lay claim to being the original inventor of another technique - one that many of us have been using since we were kids, suprisingly. I found the spectacle of a grown man behaving like this profoundly embarrassing.
The internet is a great place for sharing ideas, so if you've got one then pass it on. Two things are certain - somebody is already using it and somebody else is waiting to hear of it. Don't let the odd ego amongst the former spoil it for the latter - share the hobby!
Currently On My Stereo: Paul Rodgers - Muddy Water Blues