If you do go down this road then make sure you have a solid agreement in place with your 'handyman'.
In fairness you have experience of his work and thus far have been satisfied so maybe things will be OK.
One example from my own experience: I once subbed a conservatory and full window clean out to a Window Cleaner that was known to me. It was a little out of area and we were really busy at the time so it seemed the best option. He had four vans and six employees and had been going for 15 years. He quoted me, I added £20 and the customer booked us in for the job.
Subbie completes the job
Custy tells him he's happy
Custy then calls me and tells me that he's not happy
I call the subbie, tell him, he says the custy said all OK when he was there
I called Custy who agreed but said he was too embarrssed to say anything at the time
Subbie refused to return
As it was the reputation of my company at stake I personally went back and recleaned all of the windows (Conservatory was OK). Now I know he was out of area and was already a lost cause but we will not accept payment unless customer 100% happy, it's just the way we operate.
Now, all that for £20; NEVER AGAIN.
The custy was at fault but the job wasn't up to scratch.
Moral, be very careful when using subbies. Unless they have a good friendship with you or you can be 100% confident of their standard of work then steer clear.
Apply this to your situation and think about your recovery plan should it all go pear shaped.
I think rather than get involved adding a % I would recommend the handyman to your custy and let him charge direct. If you are determined to earn from this (and it will be a few pounds at best) then take a commision from your handyman, i.e. he bills £150 and once paid pays you whatever % you agree. This way any problems go directly to him.