Like The_Mad_Hatter, I'm wondering why you want to use Perl to do this :)

$ xev
KeyRelease event, serial 25, synthetic NO, window 0xe00001,
    root 0x3a, subw 0x0, time 13397776, (398,81), root:(1360,394),
    state 0x0, keycode 115 (keysym 0xffeb, Super_L), same_screen YES,
    XLookupString gives 0 characters:  ""
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Press keys to get their mappings.

!~/.Xmodmap will execute when X starts.
keycode 115 = F40
! run xmodmap ~/.Xmodmap to reassign the key without restarting X
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Then go into the KDE control panel and mess with the key mappings. Assign "Open application menu" to F40.