Anyone know how I can program a flexible button on a KXTA824 to change the custom service menu that incoming calls go to in a TVA50?

Today we do it though a long list of button presses that take you into programming mode (via ext *999), then to the service settings, to the custom service, to the number of the setting we need. Any way to program this long list of commands into a single Flex button?

I tried the obvious 107#6*999{password} etc, but does not let you do that...

Thanks in advance...
Rene