I had problem with SDK and other options but with FSUIPC I solved like this: a macro for FSUIPC, and then in the simulator select them as needed.

Here is the macro that has to be saved with name you decide and called in the ini.

[macros]
1=NGX_GEAR_up
1.1=C70087, -2147483648
2=NGX_GEAR_off
2.1=C74184, 536870912
2.2=C74184, 131072
3=NGX_GEAR_down
3.1=C70087, 536870912

In the simulator click your hardware up and select in Add Ons FSUIPC then under Button + Switches:
Control when sent: NGX_GEAR_up
parameter 1
Control sent when button released: ngx_gear_down
Parameter 1

etc

Should work, Luis