there is always some gimmick to remind you about crossfeed/crossflow...the fuelers used to hate me in SFO because I wouldn't crossflow on the ground. they would have to fill each wing instead of just one wing.
on the metroliner ( sa227/6) some would turn on the ignition to have the lights bright in their face at night.
during daylight I would put a piece of paper or a checklist in plain view covering up something in my instrument scan (only in day vfr at level cruise of course)...it was so annoying that one couldn't forget the cross flow. if on instruments I would hold the checklist in my hand...got old fast.
I suppose their should have been a timer to ring a bell or something...but the motto was, "crossflow once and you will have to crossflow twice">