Referral ID Default In Form

I have recently installed the Butterfly Marketing (Open Source) Script and have a tiny problem...
I am putting up a downline builder for a few great programs and all has gone well, until the most important part

If anyone could be so kind as to explain how I can use the referrers ID as default in a form, for those that do not wish to join that specific program..
Have a great day everyone!

/Roy