DISA without IVR

I have a SIP connection through flowroute.com. I have the inbound route directed to my desk extension (100). Everything works perfectly. If a fax is detected it gets intercepted and converted.

Now, I'd like to implement DISA without making any noticable changes. Can (and how) DISA be configured to work in my configuration without implementing an IVR?

Effectively, on a call, when my voicemail message gets played I'd like a button press (say '#') to initiate DISA and ask for my PIN code. Can someone walk me through? Google has not been my friend on this.

Thanks for the help.

Andrew