Just did mine yesterday, what you want is a small jeweller's screwdriver, flathead, about 1/8" (2-3mm) tip. Using a small screwdriver is better than a toothpick because it's more exact -- less likely to twist or anything while you've got it in the hole (hehe) and accidentally make contact with something it shouldn't.
Then wrap it in a single layer of tin foil, leaving maybe 1/8" of it hanging past the end of the tip. After it's wrapped, push it down point-first on the table to flatten out the 1/8" you left hanging over to make a flat-ish tip. The only reason you even need the tin foil is to give it some "deformability" to more easily maintain contact with both SL1 contacts, the hard screwdriver tip itself is too hard to keep in contact with both, especially when you've got the DS lite turned around to look at the screen.
I didn't even wrap mine since I didn't have any tape handy, but it's probably not a bad idea. There's really nothing that close to SL1 on the motherboard, especially considering the plastic surround it in the case.
As long as your tip isn't any wider than the round SL1 contact itself you have nothing to worry about. I suspect that people having shorting problems were pushing a ton of tin foil in there, or maybe the tip of their tool wasn't neatly done (bits hanging off etc. that strayed and touched other contacts)?
Still, better safe than sorry I guess.
And I did lose contact at 52% and had to wiggle it a few times to get contact back, but otherwise went perfectly. Thanks for the guide.