This will work in “Just Ride” mode using the “Reality” percentage setting. But unfortunately in Rouvy it apparently reduces the simulated gradient so your avatar climbs faster for the same power output. Unlike Zwift, where the reality setting reduces the trainer load without changing the simulated gradient for your avatar. The latter is better because your virtual climbing speed at a given power is unaffected. It is literally the same as climbing the same gradient in a lower gear.

So if you want to maintain a realistic virtual climbing pace on Rouvy then you need to keep the 100% reality setting. But if you are not bothered about that then reducing the reality setting will compensate for your higher gearing.