Yep, I use the Saitek Yoke, Throttle Quad, and Pedals as well.

Go into Settings: Controls subcatagory - Assignments: Buttons/Keys: Joystick Type= Saitek Pro Flight Yoke.

Then go to "Throttle Decrease Quickly". The default keyboard assignment should be F2.

Press "change assignment", and move your throttle lever to the negative range. Unlike the 0-100 range on the upper portion of the throttle, which acts like an axis, the red reverse range acts as a single button.

The assignment box should now say "Button 21", "Button 22", or "Button 23", depending on which lever you are using.

After this move the "repeat" slider next to the assignment to the middle, this way, you can hold the lever in the same position and the throttles will actively continue to reverse.
If you do not adjust this slider, you will have to move the lever back and forth from reverse to regular function to get the reverse to activate.

If you are flying a multi-engine aircraft and are using one or two of the other levers to control the other engines, the lever which you assigned the reverse thrust for is still the only one that will activate it, but it is helpful when engaging reversers in this case to drag all the levers to the reverse range to ensure that the throttle will not recieve conflicting signals.
(On a slightly different topic, a few addons, mainly Russian ones, like the Project Tupolev Tu-154 series, have their own joystick setup utility so you can assign reverse functions to each independent lever, and reverse one engine and not the other, along with having different degrees of reverse power, but this is a special, and nice, exception. The 154 also applies a pressure characteristic to its setup utility when it comes to brakes, in that brake effectiveness depends on how much or how little pressure I am putting on my Saitek pedals.)


This entire operational thing is kind of difficult to explain in text, so if you need more clarification, please ask!  


EDIT: Didn't pay enough attention to your second sentence in your post. In your case, I would assign the middle, blue lever, to your reverse function, and just drag both middle and right levers back when engaging reverse on the engines. Again, with most addons that do not have a third party joystick setup utility, you can only assign one lever for an overall reverse function, but it should activate it on all the engines. Just pull your engine 2 lever back as well to ensure that the unit does not receive mixed signals.

Update: Just checked, and when you are deactivating reverse thrust, even with one only one lever assigned to the funtion, you still have to pop both into the positive range past 0 for a second to fully deactivate the reverse function. If you just pop the assigned lever back to zero, the non-assigned, in your case the right engine, will still have reverse engaged.