Ok, here is what I came up with for a preliminary plan. This is going off the assumption that your trailer brakes require air to actuate, not air to release. Also since you want to keep the trailer original I came up with a plan that will allow your M1009 to have pressurized air to run the trailers air brakes.
First off you're going to need a source of air. I'd use an ARB model CKMA12 and have a tank that's around 4 to 5 gallon capacity. Wire it in so that a pressure switch hooked to the tank automatically cycles the compressor on and off. It should be pretty easy to source. Check a truck jobber. On the outlet side of the tank you're going to want to install a pressure regulator. Not having any tech specs on your trailer I can't say how much air pressure you need to put to it. If you throw 100psi at it the shoes may slam against the drum like a guillotine throwing you into a skid everytime you tap the brakes. You'll want to be able to fine tune it.
You're also going to need a pair of solenoids. One will need to be the type where if you put power to it it opens and you take power away it shuts. The other if you put power to it it closes and you take power away it opens. You will also need a check valve. It wouldn't hurt to add a filter and a dryer as well.
So here's what I've come up with as far as a way to control your brakes. Tekonsha makes a trailer brake controller called the Prodigy. An excellent piece of equipment. The output wire to the trailer brakes (what actuates them) is blue. You cut into that wire with a 3 way (on/off/on) switch. This gives your M1009 the ability to run electric as well as air brakes. You run one on switch as normal to a regular electric brake outlet at the rear of the vehicle. The other on will be for your electrically actuated air brakes. Wire in the solenoids (mentioned above) so that when you depress the brake pedal solenoid A (the one that opens with power) sends air to the trailer while solenoid B (the one that closes with power) is shut. When you release the brake pedal solenoid A closes (cutting off the air flow) and solenoid B (which is a vent) opens dumping the air pressure behind solenoid A out through a check valve. The check valve is there to ensure that only air pressure can escape the line and water, mud, etc. cannot get in and contaminate the brake system. At the rear of your M1009 mount up a gladhand and use a coil hose with a glad hand on each end to connect the M1009 to the trailer. Voila, air brakes. You'll also have electric brakes courtesy of the 3 position switch.
The Prodigy is capable of rapidly cycling electric brakes for ABS. You'll want to spend the extra money on solenoids that open and close quickly so they can keep up with the pulses from the control wire. You're going to want to find a good electrical supply house local.
While this will not be a cheap mod (top of my head I'd say $2,000 or more if you buy good components) it will allow you to keep your trailer original.
Use rubber hose (Aeroquip is good stuff) to connect your compressor to the tank. Stainless steel hard line from the tank to the rear of the M1009. Use quality components. Solder your electrical connections whenever practical.
http://www.tekonsha.com/prodig.html
http://www.tekonsha.com/instructions/BC Wiring.pdf
http://www.arbusa.com/air_compressor.php
