LED Toggle switch for ground
simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. R2 and Q1 form a logic inverter.
How it works:

The switch is unmodified.
R2 and Q1 form an inverter. When SW1 is off, Q1 is off and the EMU input will be high (assuming it has a pull-up resistor).
When SW1 is on R2 provides current for Q1's base and Q1 turns on pulling EMU input low.

One of the nice things about this is that it will work on a 5 V input or a 12 V input with no modifications.