So, if you were a big fan of superhero movies, you'd be upset when you go to see the Avengers because the ticket money goes to a company, Disney, that also produces animated movies aimed at Children? When you buy a Pepsi, do you worry that some of the money spent on the Pepsi will go to produce 7-UP?
Escape Artists is one company, that has three products, each of which a podcast. You're not donating to the products, you're donating to the company. You're asking the company to create a more complicated payment structure, which will mean more overhead and hassle for them, which will hurt all three of its podcasts.
Beyond the basic oddness of your request, I'm wondering why you assume the money is divided equally between the three podcasts. EP pays the most, per story, of the three podcasts. Since paying authors is the primary expense, that means that EP must have the largest operating budget of the three (note - I have no real knowledge of the budgets, I'm just inferring from publicly available information). And also, just like part of every dollar donated to Escape Pod goes to Podcastle and Pseudopod, part of every dollar donated to Podcastle and Pseudopod goes to Escape Pod as well. And since EP gets the largest chunk of each dollar, that means that the EP podcast benefits more from each dollar donated to Podcastle than Podcastle does. So it's not at all clear that if donations were dedicated to individual podcasts that EP would benefit from that.