[Add variable bed temperature in start gcode?]

So I have my start gcode set to warm my bed to a specific temperature before heating the hotend and bed to the final temperature.  I was wondering if there is a way to set this first temperature as a variable relating to the final temperature instead of only being able to set an exact number.  Eg, my current gcode is below:

 

M190 S55 ;Preheat bed to 55C
M104 S{material_print_temperature} ; begin heating nozzle to final target
M140 S{material_bed_temperature} ; begin heating bed to final target

G28 ;Home

M190 S{material_bed_temperature} ; Wait for final bed temp
M109 S{material_print_temperature} ; Wait for final nozzle temp

This works fine until I switch filaments that have different bed temps and forget to edit the start gcode.  I'd like to do something like this:

M190 S{material_bed_temperature}-10 ;Preheat bed to 10C below final target

Is it possible to do math in the start gcode?  I saw a couple older posts saying no, but not sure if that changed in recent updates.  If not, is there some way to do this with a post processing script?