Open ELS.ini, under [CONTROLS] section find FunctionKey = 17 and ComboKey = 18 then change FunctionKey number to 18 and ComboKey number to 17. That will switch the CTRL and ALT keys, and whenever you want to open the ELS display menu (press ALT+M to open the display menu) ambulance is not going to be dispatched to your location.
And make sure that you are running the game with the administrative rights by going to GTA IV/EFLC folder, right click on GTAIV.exe/EFLC.exe, select 'Properties' then 'Compatibility' and enable option 'Run this program as administrator', also do the same exact thing to the LaunchGTAIV/EFLC.exe (if you have Windows 8, then ignore LaunchGTAIV/EFLC.exe part).