Doing unusual Pushbacks with the current GSX version is a combination of the Pushback node you selected and the AFCAD used, because right now, GSX can only use an existing AFCAD node as a reference node for Pushback.
And, GSX doesn't support pulls right now.
About your specific case, it might or might not be possible to simulate it, using a combination of custom node AND AFCAD editing (adding nodes just to drive the GSX pushback), it's difficult to say without a better checking.
However, both the following features are planned to be added:
1) The ability to specify a custom pushback over nodes not related to the underlying AFCAD
2) The ability to pull. This will allow both an even more complete customization, but also things like transferring from gate to gate.
The two features put together, should be able to simulate every kind of Pushback possible.