That can (and is) done today - host the compiled packages in a reprepro repo, and add it as a source for apt.
If the package is a backport, apt will upgrade/install it, as it's a higher version than that in the official repo. If the package is from outside debian, apt will updgrade/install it, as it can't find any other package with that name.
I realise you said "prepackaged" but the steps to get a basic reprepro repo setup, and the steps to (e.g.) pull a testing package and build it under stable, are documented numerously online - if the existing options are too complex for the audience you have in mind, I think building (and maintaining) their own packages is not a reality for that audience.
edit: s/of/for/
I think my problem at this point is this:
Every time I have to do manual steps for something that is a one-off [which, let us be honest, I'm not going to automatically configure a deb repo since I only re-do it every few years].
Yes, it isn't /hard/ but that doesn't change the fact it consumes time I could spend elsewhere if I had a standard iso from Debian I can just spin up on a VM or a bare metal server.
Atm, my major limiter is how much time I spend building/maintaining environments vs. programming.
[e.g. Use a Debian mirror to pull from if there isn't a local substitute]