I need opinions on what to do.

I’m currently playing a Wedlocke challenge with the rules that Pokemon are not allowed to go over the level of the next Gym Leader’s highest leveled pokemon.
However, If I have no paired pokemon, only the oldest pokemon is allowed to battle.

I have three unpaired pokemon, and have no opportunity to get them pairs until after the next Gym. As such, I am only allowed to use the one I’ve had the longest. However, that pokemon will level up over the level limit as soon as he KO’s the Gym Leader’s first pokemon.
What do I do?
I can’t switch out the first pokemon mid-battle once it’s overleveled, as none of the rest of my team are able to the hit. I can’t train the others, as they are unpaired.

The only solution I can think of is to intentionally overlevel my lead pokemon so that he’s not usable anymore and then level up the backup one in his place…

Any suggestions?