That's on the wishlist, but I can't say when or if it's likely to be added.
Meanwhile, we would suggest having a page dedicated to affiliate recruitment on your Web site, so all your affiliate recruitment links would actually point to that page, and your actual E-junkie affiliate program sign-up link would be posted only there, along with whatever other instructions and info you wish. That page's URL should also be pasted as the More Information URL in your Seller Admin > Affiliate Program Settings, so affiliates can find their way back there easily.
On your affiliate info page, you could explain how to modify the default link code to show different text or replace the text with an <IMG> tag. If you wanted to get really fancy, you could even have a custom script where affiliates paste-in their standard link code, select some option or other and press a button to auto-convert their codes accordingly.