There needs to be an opening where a fleshlight type device can be accessed, not to mention an instalation panel so it can be removed, cleaned, replaced with a different model.
Of course unless the stuffing is very firm/dense, such a device would wobble in a way that would be annoying, therefore a triangluar leg brace in the shape could be installed to "hold" the fleshlight type device so the force of the thrusts is absorbed by the brace rather than just an unstable pillow. Of course a simple frame brace around the perimiter of the inside would also partially do the trick... Of course this also necessitates a secure O ring device between the fleshlight and the opening, not to mention that a slight layer of padding around said opening would dcress awarenessof the unnatural shape of the inner device...