I have both of the mech lubes from EK. I use MechLube2 for my HHKB on both the switch stems as well as when I disassemble it and lube the switch guides from underneath. Works great. Under regular use, I have to lube mine once or twice per year. Of course, I can be OCD about the board's feel and lube it more often than most.
http://www.elitekeyboards.com/products.php?sub=access,miscAfter lubing, the switches will be a bit sluggish for a couple of days. After that, it's a dream to type on once again.
Just keep in mind that a little goes a long way. But it's not critical. If you apply too much, it will just take a little longer to get the snappiness back. It's an easy thing to do and you can't really mess things up. I suppose if you did goop too much in there, you can always disassemble it again and wipe off the excess with some Q-tips. But for the most part, any excess grease will make its way down to the switch housings in the case.