Hi Kisaf, I'm afraid this is not possible from SendModelingCommand to send command in UV mode.
So it's up to you to remove the extra selected stuff or build your own grow algorithm.
A good way to achieves that could be to:
Detects uv island and give them an ID.
Store uv island ID used with the current selection.
Grow the selection in polygon mode
Deselect all polygons if they are not in the uv island.
But this not work in all cases (e.g. topology of the object is disconnected but uv are connected).
Cheers,
Maxime.