Guitar Hero Controllers permanetaly "push" left on the "d-pad".
So all you have to do is configure FMCB to also launch ESR when pressing left.
I myself boot ule with this method, which in turn automaticaly loads HDL. I am fully able to control (most of ) HDL and launch the GH game I want.
PAL V14 SCPH 75004PSTwo, fully working, XenoPS
PAL "magical" V4 SCPH 35004 PS2, 160GB, dead DVD laser, exploited
8MB official sony MC (Slot 1)
64MB chinese clone MC, Free MC Boot 1.8, Independence Exploit (backup mod) (Slot 2)