I think you should look at this question that I asked, and got answered:
PPA & Packaging: Having versions of packages for multiple distros
You'd have to package multiple times to get each version of Ubuntu, however you can upload a package for one version, then copy it over to each other version. For instance, I build packages for Lucid, however the same package is compatible with Maverick and later. As such, using the instructions in the aforementioned link, I copy it over to Maverick and Natty within the PPA, and the system then copies/builds it in the background and then publishes the data to the PPA when its done copying.