No my mistake, I got my wires crossed somewhere... but had a look into the dependencies a bit more. It looks doable but you would need to backport a lot of libs and dev files from unstable, some of which don't exist at all in squeeze. I would opt for an upgrade to testing or unstable if it's a home desktop (i.e. nothing mission critical). I'm assuming you are doing it the debian way?
# apt-get build-dep gimp
$ apt-get source gimp
$ cd gimp*
$ dpkg-buildpackage -rfakeroot -us -uc
It fails the build-dep here due to the cdbs version in squeeze, so you'd need to backport that as well... combined with the non existent libs and others which don't meet the requirements seems like a lot of work (you can get libcairo2 and one or two others from squeeze-backports)
If the mepis people haven't done it, there may be a reason why? stevepusser who posts on the debian forums builds packages for mepis and knows pretty much all there is to know about backporting, you might want to ask him.