I programmed a java plugin that does it.
Grid an image and then launch analyze particles in each of the gridded square, then you can check/add/delete the rois extracted.
I have to ask to my boss and people involved if I could pass directly my plugin, if you are interested let me know that I will ask.
Essentially, it is a for cycle where each square is used to crop the original image, then the crop is analyzed with threshold and launch particle analyzer on it and then at the end remount the montage with the rois extracted.
This the way I did it, I really dont know if I can pass my code directly due to the fact I dont know legally if I am in a confidential relationship with the researcher and the reserach campus where I work.
Have a nice day,