Yeah my testing concluded that only the AIM-54 can be launched with the WCS on STBY as the AIM-7's have the launch button not lit up while it is on STBY. Even then, because the range of the Sparrow, it isn't worth it in the first place to use a "silent" Sparrow when ACM modes like PAL exist.
For silent AIM-54 operation, you can select the radar mode prior to launch (like selecting PD-STT for a "Fox 1" guided by the TCS which wouldn't give a warning at all since it doesn't go active and allowing a loft profile while, if I remember correctly, choosing P-STT still does give an active warning when the missile is close enough for an active warning) and it will allow for totally silent operation or silent till active.