Let's differentiate between entering FM mode (can be done from a menu, by invoking .fmr, by having a special pseudo-dir in filebrowser, whatever) and being in FM mode.
The latter needs control (change to a preset station, scan spectrum, volume, ...) and has info to display (preset number out of total, current frequency, reception quality, ...) which IMHO should reside in a WPS-like screen.
You have some less often used controls (force mono, spectrum bounaries, etc.) which can be accessible from a context menu or a submenu of the main menu (cf. equalizer settings for digital playback).
BTW, same goes for recording mode.
Ideally a theme/.wps would customize all of these persistent screens.