Based on what I've now read, there is not an easy way to do this without hacking the core to turn off payment check. I'm sure I could do it, but I don't have the time to poke around. I would look at in this order...
1. administrator/components/com_virtuemart/html/checkout.index.php (try that fist! I bet it's right in there and an easy fix with an if statement)
2. administrator/components/com_virtuemart/classes/ps_checkout.php
3. administrator/components/com_virtuemart/classes/ps_order.php
4. administrator/components/com_virtuemart/classes/ps_payment_method.php
Otherwise, the other way to handle it without hacking is to apply a payment method of Purchase Order, and change the language files to make sense... something like...
radio button: Send me an detailed email of the wishlist.
This is the only "payment" option, which is now not a payment option, so they can't select anything else. Kinda cluegy, but it would work.