Go for the "Unbottle"
I have used this on several recumbents there are two ways to attach. The bag fitting between the mesh and straps on a mesh seat, or round the back of a hard shell
Firstly webbing bands work around the seat to hold in place, the other option is to use the clip to attach the bottle directly to the webbing straps of the seat if available:
The tube then runs over the seat and the shoulder of the rider. You can clip in place on your clothing, but I soon found that I would forget to unclip when getting up. Tucking it in suits me better
Edited:
I've ordered an Unbottle today. Have had a look at the seat today and reckon that the straps for the side racer pods might come in useful for securing it down behind the seat.
Great minds think alike (or fools seldom differ)