After e-junkie payment, send a http post to register user automatically?

I have the workflow thought out:

– User pays for something on your site using e-junkie.

– After payment, a http post ( with user email and name gets sent to a wordpress registration script ) and registers that user automatically — ignores if the email is in database

I think we can use the wp-register.php page for hacking! The problem I am having is having this run automatically.

I already have the option in e-junkie to send an http post after payment with (POST variables to use) automatically — but now I am not sure how to do the WordPress registration part (automatically)

Post variables from e-junkie:

payer_email Buyer's email address
first_name Buyer's first name
last_name Buyer's last name

Thanks in advance!!