SDL scancodes for rewind and fast-forward

The list of SDL scancodes includes some multimedia controls (such as SDL_SCANCODE_AUDIOPLAY and SDL_SCANCODE_AUDIOSTOP) but others are missing, particularly rewind and fast-forward. This is of concern to me because I am targeting the Amazon Fire TV Stick (which runs the Android version of SDL2 very nicely) and although most of the buttons on the remote are accessible from SDL those two are not.

So it looks as though I am going to have to patch SDL to get input from those buttons, but I don’t know how best to allocate scancodes for them. The choice of codes is largely arbitrary (I will be amending the Android_Keycodes table in SDL_androidkeyboard.c) but obviously I don’t want to make a ‘bad’ choice. Is this a case when SDL_SCANCODE_APP1 and SDL_SCANCODE_APP2 would be appropriate, or should I allocate new codes consecutive with the end of the current set, or what?