Not really. The FAA only allows the logging of instruction for legit instructional purposes....

- Training for a rating
- A/C fam
- Route/area fam
- BFR/IPC
- Club/insurance checkout


If you fly multiple XC legs and log all of them as dual, that is obviously not realistic.

Since you are the MEI and actual pilot is not an MEI, it would be ridiculous for YOU to jump in an airplane you've never flown, that this guy has been flying for years (?) and give him dual on routes he has flown hundreds of times. Don't do it.

The only legit way to do this is for you to fly whatever legs he lets you fly, and log it. But there's a few catches...

1) You have to be PIC and manipulator.
2) He cannot log your legs (he may not need/want the time anyway)
3) If insurance requires him to be the PIC (it will), then you risk voiding the insurance coverage.