Has anyone ever succeeded in getting 2degrees to redirect to something other than voicemail when unavailable?

We have 6 work phones with 2degrees, and we want to direct them to our message service, not 2degrees voicemail when we're unavailable. The stores and contact center tell us to run #21# which is divert, always on - not exactly what we want because then we get no calls at all. Tried turning off voicemail and enabling "divert when unavailable" on the phone, but we still got 2degrees voicemail, just with a message that voicemail is disabled!

I know Spark can do it as many of our clients redirect to live message services, but moving our phones to another provider is the last thing I want to do. Any ideas?