Here is what you'd have to do to get a XL CE2 to work:
1)
buy some Polycarbonate tubing. You can get it from McMaster-Car.
2) Cut a short piece of the CE2 stainless tubing and place it in the top cap of the Lavatank.
3) Place the CE2 in the bottom cap and slide the top cap (with tubing inserted in it) on the top of the CE2
4) Measure the distance and cut a polycarbonate tube to length.
The only problem I see with doing this is when you need to refill. When you take the top cap back off, I see one of 2 things happening. Either the CE2 will pull out of the bottom cap or the silicone cap you stay in the stainless tubing and you'll have to go fishing.