propposed way to do this:
* install depends and makedepends before running `makepkg -sr`
* run `makepkg`
* install depends and makedepends from the next pkgbuild
* run `chcleanup` with a concatenation of clean system and current depends, this will remove the dependencies from the previous pkgbuild
* run `makepkg`
* etc.

it's not perfect but it would ease things a little.