I've never had the problem on a recumbent. However, I did replace my Bacchetta filter foam seat cover with a comfort thickness Ventisit pad. I find the Ventisit much more comfortable in providing better ventillation, no increasing deformation over a longer ride, about the right trade-off between enough friction to hold you in place yet slippery enough you can slide small amounts when you want to, and eliminates your jersey snagging on the cover. I even ride it shirtless when the bike is mounted in the trainer, something that would be uncomfortable with the stock filter foam. However, it is a $100 investment to see if the Ventisit works for you.

One alternative is that Bacchetta now makes a woven cloth cover for the filter foam. I believe this costs less than a Ventisit and because it covers the surface of the stock filter foam, this cover is reported to eliminate the itchy/scratchy surface. I doubt it ventillates as well as the Ventisit.

The other thing to try, possibly in conjunction with the Ventisit or cloth cover, is to add some padding to portions of the back of the seat, thus changing the contour of the seat. This may distribute the pressure more evenly, taking some of the load off your shoulder area. Some cyclists use a drawer lining material that is rubbery and is perforated in a checkerboard pattern. This is layered underneath the regular seat foam/pad to provide varying thickness as needed. Others (including myself) have cut out curved contour sections from firm packing foam and put them underneath the stock foam for more support, usually in the lumbar region of the seat.

Do please let us know if you find a solution to the problem.