Dual pricing 1.5 on 1.3.0.1?.. help me!

:DHello Everyone!
Got a 1.3.0.1 working, heavily modded and "bolted into" google, so i dont want to mess with it.
I was wondering, is there a way to add dual pricing 1.5 (features wise 1.5 is good for me) to a 1.3.0.1 installation?
Upgrading the whole shop will be too long for this simple task.
Anyone got any ideas?
THANKS!

You realize your shop will break when your host upgrades the php version on your server? You need to keep up with current versions.

Hmm...ok...
I agree, so let me ask you this..
Is it possible for me to backup my current DB, upload a fresh install 1.3.8 to the server and "inject" the old material into the new installation?
this way, i can call the new installation directory "shop2" and when its done.. just change the folder name to "shop" and voila..tranparent upgrade?
Is there a way to "import" customers/orders/products from an old version?
thnx