The proper way to do this is to first make sure that the package uses a patch system, and if it doesn't set it up to use Quilt. There should be answers on this site for how to do that.
Then, create a new version of the package using dch -i. Add your changes (such as use of a patch system) to the changelog, add your patch into the patch system, and then test the package (locally or in a PPA).
From there, you can attach a debdiff to the bug report, tag it "patch", and start hunting for a sponsor. A debdiff makes it very easy for a developer to just see your latest version of the package (patch included) and upload it themselves.
You could skip some of these steps and just attach the patch to the upstream source code to the bug report, but then your sponsor would need to do them all for you, and that means it'll probably take longer and it'll be harder to find a sponsor (since your package seems like an uncommon one, it's likely no developers are even familiar with it and thus might be reluctant to apply a patch).