You can do it with a JR8103 is you use EITHER P-Mix 5 or P-Mix 6. Both of these mixes will have a "trim include" function automatically built in. When you mix 2 chanels--they both respond to trim inputs.

Go to P-Mix 6
Set ELEV as the Master and GEAR as the Slave
Hit the select button to move the arrow / cursor down to the mix rate
Move your elevator stick UP (down elevator input)
Push the + button to set the mix rate at 100%
Pull your elevator stick back (up elevator input)
Push the + button to set the mix at 100%

Now you need to disable the GEAR switch on the top left of the TX or it will make your elevator move if you accidentally hit the switch.

Simple:
Go to Travel Adjustment
Select the GEAR
Set travel to 0%
Now flip the Gear switch on the TX to the other position
Set travel to 0%

Your almost done.

You need to use Sub-Trims to fine tune the center of the servo at neutral. Just go into your Sub-Trim menu and use the + or - buttons to center up the servo at neutral.

Go fly.

6102 won't do it. 652 won't do it. The new Spectrum 7 channel WILL do it. I am not positively sure about the 7202, but I think it will do it.