The idea is to fake the UX without storing anything permanently. Generate a temporary ID to store data to while the user is playing with the site. If they've added ideas they want to save permanently, overwrite the temporary ID with the new user ID. Storing the data only matters if they sign up. I'm a programming noob myself, but I think this should work. If I'm dead wrong, it should only take a couple minutes for me to be corrected ;-)
A little inspiration: splendidbacon.com/
Congrats on building something cool, btw!
EDIT: Go to account and look at the email address... it's randomly generated. Cool, huh?