Did you backup Lion to Time Machine? (I'm not sure if you can tranfer data (see below) from a Lion TM Backup)
If so, make a clone first with CCC or SD (A good idea to do it anyway)
Boot from your Snow Leopard Install Disc
Select [Continue], then in the Menu Bar, select Utilities->Disk Utility
Highlight your Mac Disk (not volume), and click the Partition Tab
Set the format to Mac OS Extended (Journaled)
Click [Options], and set scheme to GUID
Set the Number of Partitons to 1
Click [OK] (You did say you have a backup. This will wipe all data)
Quit Disk Utility
Now n the Menu Bar, select Utilities->Restore System from Backup (If you did not backup Lion to TM)
or:
Select: Install Snow Leopard
Plug in your Clone
When prompted to transfer data, select: Time Machine or other drive (your Clone)
After Install, when you boot into Snow Leopard, select: ->Software Update...
P.S. There is no easy way 😉