To do this, you need this command to launch using the Shell verb "runas".
You can download a reg file here.
http://www.winhelponline.com/blog/register-dlls-elevated-using-the-context-menu/
REGEDIT4
;Register modules (Elevated) from the context menu
;March 25, 2008 - (c) 2008 Ramesh Srinivasan
;http://www.winhelponline.com
;http://www.winhelponline.com/blog/
[HKEY_CLASSES_ROOT\dllfile\shell]
@="none"
[HKEY_CLASSES_ROOT\dllfile\shell\runas]
@="&Register (as Administrator)"
[HKEY_CLASSES_ROOT\dllfile\shell\runas\command]
@="regsvr32.exe \"%1\""
[HKEY_CLASSES_ROOT\ocxfile\shell]
@="none"
[HKEY_CLASSES_ROOT\ocxfile\shell\runas]
@="&Register (as Administrator)"
[HKEY_CLASSES_ROOT\ocxfile\shell\runas\command]
@="regsvr32.exe \"%1\""