The IFR C206 in front of MDX had no problems planning via WLM.
If I remember correctly back then when you submitted a flight plan you would plan via SGT MQD (inbound to SY/BK) and via WMD (outbound). However you could include via WLM as an option/preferred tracking. If you included this option in your flight plan the Briefing Office/FSO would include WIlly they sent the flight plan to the relevant ATC units.
The flight progress strips (blue outbound, yellow inbound) would include a note of the overhead WLM option/preferred tracking.