I have the 45 mm , but from Panasonic and the 60 mm from Olympus of course .
I don't see any interest to try to use a micro fish eye lense which is built for macro wide angle with a macro lense especially the 60 mm from Olympus which is a film 120 mm .
On the macro mode position of the 12-50 at 43 mm it dont' work , so I suppose that it'll be the same with the Panasonic 45 mm that I own also but I have forget in France and I 'm staying in the Philippines untill May ,.but I'm a sure that it won't work , the camera can't make the focus through a macro lense and the micro fish eye .
I've use it with the 12-50 in between 40 and 50 mm ( no vignetting ) ( 80 to 100 mm film ) and that match with what tell Inon .
I'm not very enthusiatic at the idea that I'm going to show not good picture , anyway if it can help you !!
This one is not cropped , no change in any way , 44 mm with the 12-50
This one also not cropped , although the subject is not really CFWA , taken also at 44 on the 12-50
This one has been taken at 39 mm , you can see the vignetting appear no crop
Of course if you are in the blue ....
The good thing with that combination , is that you can obtain suns not too burn !! I wonder why ... ;-)
This last one at 50 mm , not cropped as the other of course