I would take that as a challenge:)
I bought a LaCie external disk, checked it was formatted as Mac OS Extended (Journaled) and have cloned my hard drive to it with no problem whatsoever. (I used Carbon Copy Cloner but you could use SuperDuper or just from Disk Utility)
Well, looking at this forum, it looks like you may need to do the re-partition thing to get the disk to renew its index.
Since this needs to be from outside the disk and you need good backup anyway, I'd get your data up-to-date, copy the installer to another folder on it, so it doesn't disappear after the instal, buy an external disk atleast the size of the computer disk, clone it to your Snow Leopard, boot into it, use its Disk Utility to check permissions and Repair Disk on your computer.
When you are ready, re-partition it (this is the point of no-return because it wipes the disk)
Now you can do a clean instal to a single partition which gives you a good chance of having a nice computer with a Recovery HD to boot (excuse the pun).
Then boot into your Lion and use Migration Assistant to move your data and apps across from the SL clone...
Put the SL clone in a safe place and forget it.