Removing MS Security Essentials with SEP 12.1.5 deployment

Deplying SEP client including '...automatically remove existing security software' option but MS Security Essentials seems to be staying put. According to the Third-party security software removal support list.pdf, Security Essentials version 4.0.1526.0 should be removed but x86 only. The version I am try remove is 4.5.216.0. The two versions use the same numbers...coincidence? Also, I'm dealing with mostly x64 devices.

My local Symantec guy says sepprep will do the job but looking at the included .ini file, there's no mention of any version of Security Essentials. Not been able to give a whirl yet but does anyone know if it will work?

Is there a better way of moving that software? There's no system management tools (SCCM, Altiris etc)

Thanks