To clarify, in my writings "participant" would apply to both, a distinction from casual observers, not at the degree of involvement.

For me, if a person holds a coin they move from being a 'spectator' to a volunteer, referee or agent.
Most importantly, them now serve as a witness for the guy in the back row.

I was attracted to the thread by the title "spectator does the magic" as that does not make sense to me.
So, I started watching posts here to better understand what other consider to be "one who observes" vs. "one who participates in the action."

I though the OP was looking for examples of effects where the audience would consider that the 'volunteer' "did the magic," with OOTW just an example -
that is, I though he wanted more, not just similar tricks. I do not agree that "only one may feel..." My experience is different there.
If you ask a 'spectator' to say a magic word or blow on a coin, they might well feel they were a cause of the magic. "Concentrate?" - not sure,
but in many Mentalism effects that is what happens. In conjuring I find it best to have the Participant verbally say something like, "I now hold the silver coin" before opening their hand.
But, I am not above also saying, "He seems to have some difficulty focusing. Why not everyone mentally send him some magic energy to help the ring get off of the string?"

My objective is always to provide "a real experience of magic." Getting as many folks to become Participants rather than passive Spectators works for me. Perhaps not for others.
So, I offer examples based on my experiences and hope they will help the OP and others in their search.

Wravyn - send me an addy to ken@eversway.com and I'll send a copy of "Untouched."

Harry Lorrayne did Lazy Man’s Card Trick. A perfect example of spectator thinking they do the trick. I

https://m.youtube.com/watch?v=tPL0jD506cs

Not participating, not saying magic words, not sending energy. Doing the magic. It isn’t a tough concept.

Adults do not believe in magic. They know we are doing tricks as a rule. They chose to suspend that belief. But treating them like 6 year olds doesn’t help them take you seriously in the least. The only one fooled that way is the magician.

This thread has been very interesting...I never differentiated between the spectators "doing" the magic, and the magic "happening" in the hands of the magic. I guess I saw them as the same. This discussion has got me rethinking things...

Thanks all!