You can put EXT0_SELECT_COMMANDS "M340 P0 S1540 in the start g-code to ensure it is run at startup. These commands seem to be run only when a extruder is selected but that is not the case at startup since extruder 0 is already active.
Also note that you have no wait afterwards and no disable of servo after a time. First could lead to starting print before servo is in position. Latter will keep servo on all the time. That could cause jitter effects depending on how your system works. Problem with servo disable is that you need power at startup to move servo in any case. Most boards can be configured to only work from main power and not from usb, which is what you need here.
