FVWM: Define menu-entry as disabled (greyed out)

Greetings!

How do I define a menu-entry as disabled—e.g.: iff a window must not be
re-sized the “Resize”-entry in FuncFvwmWindowCommon is greyed out
automatically: but how do I do that on my own?

I am aware of the Test-Command in menus, allowing me to not enter an
entry e.g. iff the executable is not executable:

...8<---
DestroyMenu TestMenu
AddToMenu TestMenu "Test" Title
Test (x some_executable) + "some executable" Exec exec some_executable
--->8...

But how would I use a Test-command to add the entry disabled and “greyed
out”?

Thanks in advance!
 Kalten
-- 
fvwm 2.6.7 compiled on Dec  1 2017 at 15:23:15
(ReadLine, XPM, SVG, Shape, XShm, SM, Xinerama, XRender, XCursor, XFT, NLS)