There's unequipping as noted, but that's considered somewhat socially gauche by the community - mainly because so many people are bored of getting the lowest level roulette picks so often).

The "acceptable" way to limit your dungeon selection on Roulette, is to bring a friend with you who legitimately only qualifies for fewer dungeons. That is somehow perfectly okay, even though it also results in people getting stuck with the lowest level roulette picks so often.

(Frankly, the whole dichotomy starts to remind me of my younger brother, who would insist things such as that it was cheating to look up guides but okay to have someone else look up the same info in the same guide for you. LOL)