I've never given any thought to "left pair"/"right pair" engine lever control.
But it must make sense to you.
First. Do you have
FSUIPC? It's payware, but if you want more out of FSX, you need to put something in to it. Money, usually.
If not then this will be a total waste of time.
It may still be a waste of time, in that I use FSUIPC to send 2 commands with
ONE BUTTON and not levers. Still, it may work.
I have TrackIR. Inside a VR cockpit it's one of the greatest flight sim add-ons around.
But when I switch to an outside view, it's irritating. You look left/it turns right. You look right/it turns left.
So when I hit the button to switch to an outside view, two things happen.
FSX has been instructed to switch to an outside view when I hit that button. It's a simple button assignment
in FSX.
BUT in FSUIPC I've set that button up to send another command through SimConnect. TrackIR receives a button command to PAUSE TrackIR.
When I switch back to an interior VC view, TrackIR receives a command to resume. One button, two commands.
But you want to use levers/axis for two commands.
This is the area where,
if it can be done, you want to look.

Good luck.