Plugging from a certain category?

How do you plug commenters from the last blog from the same category?
I was wondering if there was a “hack” at all :/ because I would like to plug people from my past blog in the general category. but i “blogged” some other stuff in the other category and if i blog in the general category now it will plug the other commenters from the last time i blogged…
And i don’t really want to do it manually :/
umm ill elaborate when someone doesn’t get me lol