apturl (the magic program that handles
apt:// URLs) does have code to handle
apt+http:// URLs like this:
Which would theoretically add that PPA, install that package and then (if the user wanted it), leave that PPA installed.
apturl's manpage currently says this is disabled:
Warning: This is currently disabled because of security concerns.
I've just tested it and it does appear to be disabled. I can understand the security issue. Having people install software from PPAs is enough of a security issue let along making it a 1-click operation.
The alternative for people who want to release a PPA for their own software is to write a dummy-package that adds the PPA and installs the other packages. You either make that .deb available on your website or you could ask for it to be added to the universe. Then it really would be a 1-click thing.