I've ridden in mismatched situations on several occasions.
For several years, relatively recently, my father and I would ride together and during that time I was stronger with more endurance. (The tables have turned now, and he's the stronger one ... but we'll see about that.

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1) There were several times where I planned out a route that included an "escape route" ... and he joined me for the first ½ of it, then returned home on the "escape route", and I continued on to finish the whole thing.
2) Or I planned a loop route of 3 loops, and he’d join me for 1 or 2 of them.
3) Or I’d plan a route, and go ... and he’d leave an hour or two later and ride the route backward to meet me, then ride with in with me.
4) Or if we were on an out-and-back, he’d turn around at a certain point and I would continue on to another point, then turn around and ride back … trying to catch up with him.
5) Several years ago, a cycling friend and I were also mismatched, with him being stronger. He finished work an hour before I did, so he would set off on a particular out-and-back route an hour before me, and would ride hard to the designated turn-around (approx. 40 km down the road), and then turned around and rode hard until he met me. Then we’d either keep riding a little further out, or would turn around and ride back, depending on how I felt.
6) Occasionally, I would set off half an hour, or an hour or so, before my cycling partner, and he would ride hard to catch me.
7) During the time we rode together, I wanted to do intervals or something to help increase my speed. So we came up with this game.
We had a beautiful, smooth, 3 km square loop, with a couple streets dividing the loop to make it shorter if we wanted. I'd start somewhere at one side of the loop, and he would start at the other. I would ride hard to keep in front of him and he would ride hard to try to catch me ... then we'd do a recovery loop or two before starting again.
That was THE BEST way I've ever done intervals!!
8) Another idea might be for the stronger ride to ride hard to the next intersection, then turn around and ride hard back to the slower rider, then cycle with the slower rider to the next intersection for a rest, and repeat.
9) Or do side excursions. I’ve had a couple cycling partners do that … when they see an intersection in the distance, they’d ride hard to it, then ride up it a way and back, then ride hard to catch up to me, wherever I was, and then ride with me for a while to rest. Sometimes I just let them go and kept going my same pace, but now and then, I tried my best to hang onto my partner's wheel for as long as I could.
10) Also see if there are any multi-distance cycling events coming up. The local century often has 50 km, 100 km, and 100 mile rides. Sometimes they set it up so that all the riders can ride some of the event together before they split off and do their own thing.