Most tandem teams ride without IPS.
Until we moved on up to the 'bent tandem this year, either my stoker or I would periodically call out for a "Butt break!" every once in a while, signalling a cessation of pedaling and a rising up off the seat, just for a moment.
Double your pleasure!
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Bacchetta Giro A20, RANS V-Rex, RANS Screamer