is there any way to do this? I have the textless mana leak that I want to list, and it's worth a bit more than just a mana leak...
Also, is there a way to mark a card as foil?

In your tradelist, you have the option of entering card details, just as you do in the main Inventory screen (in fact, you can specify versions there).

I believe there are some hiccoughs with the way those details affect what people see as available in the trade window. Sebi and the team indicated they will be updating that interface later this month.