Re: running a program from debian/tmp
For some value of easy... I think most people who work with Debian packages on a regular basis use a chroot environment to build and install packages.
Several similar programs can be used for this: pbuilder (and the faster copy-on-write variant, cowbuilder) and sbuild are the ones I've used in the past. I'm sure there's many more. But it's not exactly an easy way of doing it, since some initial setup is required (bootstrapping the Debian base system environment)