quickly turn firewall on and off

I believe you can use the buttons on the right to add services (and ports) which are not listed as options. I can't tell you exactly how to do it because my firewall is configured separately so all the options are greyed out but try "New".

- cfr

System Preferences>Sharing>Firewall>New.

Do you know why you need to allow incoming connexions for DW? It isn't that I disbelieve you. It just seems odd. One way of telling what's causing problems is to set up logging for the firewall (I think it is under "advanced") and then to see what happens in the log file when you try to access whatever and it doesn't work.

You could script starting and stopping the firewall. The trouble is that if the System thinks you are managing the firewall settings other than through System Preferences, it will grey out all the firewall options to avoid a conflict. It is not then enough to stop the other software - you have to reboot to get the System Preferences interface to work again.

I'm not sure exactly what it takes to convince it that other software is configuring the firewall so I don't know exactly what you can get away with.

A direct command line approach would be:
sudo ipfw disable firewall
sudo ipfw enable firewall

However you do it, it won't be one-click as it will require authentication.

The other possibility might be to use the defaults command to manipulate the preferences.

- cfr

If you find out what ports are needed to be opened you can do that and still maintain the firewall.