Probably a simple apache rewrite rule but i just can get it to work. Help if you can!

What it is;
Webmaster place links to my site using the following link;

https://secure.ibill.com/...p://www.mydomain.com

I don’t want them to click on this link because it isn’t a direct link to my site and therefore won’t help my Page Rank in Google.

I want them to link directly using to something like;

http://www.mydomain.com/ispyxxxxxx/

ispyxxxxxx being unique for each webmasters link.

What would my rewrite rule be to have user click on http://www.mydomain.com/ispyxxxxxx/

Then redirect them to https://secure.ibill.com/...p://www.mydomain.com

Using the ispyxxxxxx from the original link as the variable.

Thanks in advance for any help.

I have tried RewriteCond %{REQUEST_URI} ^/ispy
RewriteRule .^/ispy(.*)/$ https://secure.ibill.com/...p://www.mydomain.com