It can be done, if you jailbreak your Kindle first.
Here is the user-friendly hack ("updating" via .bin file).
Before trying anything read the thread or at least read the included readme.txt file carefully! And keep in mind that, if I'm not mistaken,
this hack was not tested (nobody gave feedback/confirmation in the hack forum thread) on Kindle 2, but it was confirmed as working on Kindle DX with firmware 2.5.8. So it
should work for Kindle 2