Hi eagle,
nb store needs to return to the checkout module to finalize the payment (update it as paid/not paid etc).
The configuration of the reruen page is done in the "PayPal.gateway" template in the backoffice. Look for the <ReturnURL>,<ReturnCancelURL> and the <ReturnNotifyURL> tags.
Maybe you could create another page with the style of page that you are looking for, but I am 90% sure you'll need to include the checkout module there as well to update the order status.
I haven't done this myself so I really don't know if it will work.
I hope this helps and gives a clue to what you are trying to do,
Geoff