I found a workaround. If you need to install build dependencies for package X, just create a fake package, which has "Depends", which are equal to X's "Build-Depends". Then install this fake package via aptitude.
Possibility of such workaround means that aptitude already has all needed machinery. We just need to make aptitude to treat "Build-Depends" in similar way to "Depends" -- Askar Safin
