Mach3 solenoid control, how best to trigger multiple solenoid outputs?

Hello,
This is more about ways/options of setting up the software/code for my situation:
I built a custom machine, 3 axis, with the spindle being replaced by 3 air solenoids on the outputs of the board (generic mach3 4axis breakout board, sainsmart). They all work good. I call out M commands to activate them (m3,m4,m7) and m5 to deactivate. I am thinking of using a plasma post processor script to run in Mach3 like this generic example:
M3 (Plasma On)
G4 P1.0000 (PIERCE DELAY)
G1 X38.0368 Y24.1868 F1500.00
G3 X40.0000 Y25.0000 I38.8500 J25.0000
...
M5 (Plasma Off)
But I need the post processor to call out m3,m4,m7 as if they were acting as a new tool (the 3 solenoids are spraying different color paint, they're permanently mounted too). Imagine as if my machine has 3 plasma heads being used throughout the program (not simultaneously btw).
I was floating the idea of calling out a tool command (T1, T2, T3...) in the post (the gcode file mach3 runs) and M3 activating the solenoid based on which tool is currently active (could this be done in mach3 where, based on the active tool, M3 could call out a different output pin?).
The post would look something like this:
T1 (call tool 1)
M3 (start spindle command--activate solenoid 1, which would be output 1)
...XYZIJ... (general machine movement)
M5 (stop spindle, shut off solenoid valve in my case)
T2 (call tool 2)
M3 (activate solenoid 2 on output 2)
...XYZIJ... (general machine movement)
M5.... (shut off solenoid valve)
AND SO ON...
I am looking for general advice or a resource to point to, the forums gave a little insight but my situation is a bit different.
Could there be another way to set this up? Ultimately, I just need 3 solenoids triggered throughout the code (which spray different color paint).