Well I think I'm getting somewhere with this - it looks like I can configure an input pin to send OEM code 301, which I can use to launch a Macro I define? The Macro would be able to press the 'cycle start' button through code, plus activate an output for the indicator.
In General Config->initilialisation I would run a Macro (saved as M700, say) which sets the macro associated with OEM code 301 as follows:
SetTriggerMacro(M701)
Macro M701 would contain the commands I want to run.
What I can't figure out is if there's a way of having more than one user-defined macro accessible from the input pins - since I'd need a separate macro fo the 'Cycle Start', 'Feed Hold' and 'Stop' buttons. Or do I need to link the same macro to multiple pins, then check which pin called it from the VB Code?