The jam rag may be moved to the side during the act, or a male with a specific fetish might simply abraise their member against the padded liner for one-sided pleasure.
It is un-usual for the female to be aroused during this manoeuvre but not un-heard of.
Jimmy: Then why are you smiling?
Johny: Because I'm gonna rub my knob against her jam rag tonight!
Jimmy: OMG You're such a Jam Rag Joyrider mate... Jog on!