@jeanineonthecamino points and questions are excellent. I will share my experience with you and hope it helps:
I have done this on the CF, I the walker, my partner the biker. A lot of the time he would get off his bike and just push it (it was easy to do in low gear, the bike carrying all his gear), walking next to me. Or, he would bike alongside me at an absolute snails pace (I don't know how he did not fall over with so little momentum forward) for as much of the day as he could.
If he saw the path became too trecherous to ride his bike with me, he would take to the streets, re route himself and meet me up ahead (sometimes a half hour, sometimes 2 hours, etc). He used my guidebook and some biking apps on his phone to figure out how to reroute himself. Other times, if he thought the bit of trecherous path was short, he and I would push the bike together up a steep way or over awkward rocks, etc. then resume together. And yes, he spent a lot of time "up ahead" in a town or under some random tree on the camino, waiting for me. Was he bored or lonely? Don't know, he never complained, but I know him to be a chatterbox who made friends with anyone. And, he had a cellphone to hop on to for entertainment and for research (looking ahead at other parts of the path).
I was committed to walking & carrying my own gear despite injuries and so taking a bus or taxi up ahead was never even considered by me, or suggested by him. We stopped multiple times a day to rest because of my knee injury and tendonitis. There were many days when we stopped early altogether because I had reached my limit.
As you can see, much of this operation revolved around me, the walker.
Was any of this planned for me or him? No. We met at the halfway point on the CF and this arrangement came to be. I was a solo walker. He was on a journey to bike Spain & Portugal. It was made possible mostly by his patience, flexibility, and mutual romantic feelings. It was organic and felt right, even if you'd argue it was "inconvenient" for him or that I gave up too much of my solitude or something(?).
I don't regret walking half my solo Camino with someone else (does anyone regret embracing their "first love"?), and I don't think he regrets slowing down to do it. But I don't think I'd ever plan a journey like this, or go out of my way to try to make it work with someone else walking/biking. I think it will take a real specific type of biker and a real compatible pair of people to make it work like we did, with no conflict, complaining, bordem, resentment, etc.
If you're willing to give it a try and are prepared to deal with some of these inconveniences as the biker, and believe it will still be worth it for you & your friend, then go for it.