If the purchasing has to be done at the company's site, there's no choice. Some people I know who do MLM (party supplies, dental stuff, all different kinds) also have to send shoppers to the company to purchase. So then, a remote cart like Mal's or PayPal isn't even necessary.
It can be set up just like you'd set up an affiliate site. You just do flat optimized HTML pages geared to some specifics, with links to the company, just like you'd do if it were a regular shopping cart. They're like a little "mini-site."
I've been talking to some gal who's got an MLM coffee site (no traffic, no sales). She and all the others in that bunch use the same wording as the parent site does, which isn't worth a hill of beans. All it's worth is the inbound link they get as a distrubutor. They sell direct, so they have to buy the kit.
I wanted to know, so I asked her if when they're with that company they can do affiliate programs on their sites. She can - some allow it, some don't. There are only two phrases that can be used, so setting up related affiliate stuff would broaden the possibilities for her. No problem if it's not allowed, it's easy enough to get around that one. I'll probably point her to some gal who heads up a couple of MLM groups for WAHMs.
hasbeen, get her the site done up and then send her off online on her own to do some "relationship marketing" at women's communities. It's fertile ground for picking up a downline for those who learn the ropes.