A general solution is putting a notice on your PPA description for users to manually install newer version, e.g. "install Django 1.4.1 via this PPA first: [...]". However, I can't seem to find any semi-official PPA providing this latest release of Django.
For Quantal (12.10),
1.4.1 is already included in the main repositories (
python-django in Quantal). So, try to re-build the regular Ubuntu package for Precise and put it in your PPA. That seems to be the easiest and best way in your case, I think. More people can profit from your work of backporting this Django version for Precise! It also allows you to set a clear dependency on your package.
I would avoid any scripts downloading and installing packages from source, unless licensing issues are forcing you this way - e.g. Adobe Flash, Oracle Java, MS fonts, etc.