"This program allows me to automatically open a BiaB song for accompaniment"
So are you using the "MobileSheetsPro Companion" on Windows ?
"Open File in External Application – Loads the file that was linked to the smart button in an external application. If no default application is assigned for the selected file type, you will be prompted to select a supported application to load the file."
Can you select 2 Files to open ? if so you can create an AutoHotkey script Biab-Gen-Play.ahk to send Gen/Play command to Biab.