I sort of used this idea in my 801 and 901 carts (I'm not fond of round tips). I'm not sure if this idea has been done before, but here goes anyway:
I put the spring in vertically, instead of sideways. I used a small piece of white AquaClear aquarium filter insert foam instead of blue foam or cotton, or whatever else. It seems to work really well, but tastes horrible when run dry. I believe these filter inserts are plastic, so my guess is that they'll last.
The springs help keep the juice in contact with the atty. The filter foam wicks really well.
With this mod variation, especially with the 801 high-bridge atty, the foam can get pushed in, but it'll bounce back when the cart is removed. Prior to using this mod, my 801 high-bridge atties were just not working well with carts, and I was getting very frustrated. Problem solved. This seems to work a lot better than regular carts with my 901 and 510, too.
(Well, I haven't tried it on a 901 atty yet, but I have a 901 cart on my 510.)