if you have 40 fixtures with individual DMX addresses, as you said you will not be able to patch them in the B-station, as, as you said, it is limited to 32 fixtures.
But, I can see a solution if your fixtures are not too complex.
You can use the DMX task, and use the RGB-BLOCK, it will set all the fixtures starting from a specific DMX address to a specific color. You will probably have to add a task to set the intensity to the right level too.
But it should fit your expectation,
Then just make a DMX/clear when the ARt-net comes back to clear all the DMX values..
I hope this will help you,