There really ought to be a way to /showmirc -n or -t (minimized or tray) and specify that it goes into Lock Mode as if you were holding the CTRL key./showmirc -nrstxoplL
Manipulates the display of the main mIRC window, where -n = minimize, -r = restore, -s = show, -t = tray, -x = maximize, -o = on top, -p = not on top, -l = minimize & lock
, -L = tray & lock
This suggestion posted
on the Feature Suggestions forum.