Add i-frame to shopping cart

I have two websites, one using zencart, and another using cubecart. Both use a mals-e payment processor plugin, so that orders leave the shopping cart, and are then transferred to the mals-e .com site, after which they are transferred to my payment processors. I require the mals-e modules for the zencart and cubecart to be modified such that they point to an i-frame inside my website. I'm aware that it is possible to bypass the mals-e portion of the process, so please don't bother giving advice about that. My required solution is to integrate the mals-e portion into the look and feel of the website. There are discussion forums that discuss such implementations, such as the mals-e forum, so help will be easy to find.