Yeah, if the snakes are under about 5g, they probably can't eat even the smallest pink. But to be honest, I'm kind of squeamish about dicing up pinks myself, but if you cut them lengthwise in half (right down the back) while the pink's frozen, it is surprisingly un-messy. I do that, then I dry thaw them. I put the pink halves in a little plastic cup and float the cup in a larger cup of very hot water. Then I swish them in the fish juice (see above), and offer them. Even though my garters are only about 4g, or maybe a little more, they both ate two pink halves earlier tonight. The total weight of each meal was about 1.5g (equivalent to a small whole pink). And boy did they look stuffed afterward. I think you could handle the cutting. Believe me, I'm not into the extreme stuff either-- if I can do it, you can do it.
I haven't read of any particular brand of supplement being recommended for garters. I imagine that Rep-Cal's Herptivite is suitable, and it's available almost everywhere. I know it contains vitamin B1, which should help combat the thiaminase business I mentioned in my earlier post.
And speaking of thiaminase, I did some more research, and some sources say that red minnows are chock full of it, while other sources say that they don't have it. I don't know who to believe on that one. I guess that trout, salmon, pike, bass, and many other sports fish don't have it. But if your snakes demand live fish, those are out. I also read that if you offer a worm-exclusive diet, you need to supplement with calcium as well as vitamins. And you shouldn't use trout worms (I think they're also known as red wrigglers or composting worms). I guess cut-up nightcrawlers are best as far as worms go.
Those rodents are sounding better and better, eh?