The Uim-tool can switch to use Qt or gtk, but it's package currently is dependency gtk in Platform repo. Please to change it's dependency from gtk to qt.Uim tool example in offical wikiUim for Qt in ccr
You'll need a package database if this is the way you want to do it. Take a look at repo-add and related utilities if this is the way you want to manage your packages.Personally, I prefer to install aur/abs packages using pacman -U with the --asdepend switch if it is a dependency of another package. The dependency status is carried over for a package update, so it all works out.