New versions can be backported by following the Ubuntu Backport process. Ubuntu doesn't accept binary uploads. Also, PPAs do not provide binaries for arm, only amd64 and i386.
The simplest way to proceed is to use the requestbackport tool from ubuntu-dev-tools.
An example in this case would be:
$ requestbackport -d precise -s quantal gimp
Which provides the output:
requestbackport: * LP: #1006424: Please backport babl 0.1.10-1 (main) from quantal https://bugs.launchpad.net/bugs/1006424
requestbackport: * LP: #1040756: Please backport fftw3 3.3.2-3.1ubuntu1 (main) and fftw3-mpi from quantal https://bugs.launchpad.net/bugs/1040756
requestbackport: * LP: #1006426: Please backport gegl 0.2.0-1ubuntu1 (main) from quantal https://bugs.launchpad.net/bugs/1006426
requestbackport: * LP: #1002780: Please backport gimp 2.8.0-2ubuntu1 (main) from quantal https://bugs.launchpad.net/bugs/1002780
So, you can see that the request has already been started in LP: #1002780.