I can’t think of a way to do it using standard tags- leaving off the row/col will result in the default of ‘3’ being used. Thus the only standard option would be to up the col/row to as high as you’re likely to need.
You could work around it using a query- and it would likely be possible to use some php to come up with the actual number of rows/cols needed to fit all of your images and use that in the standard tag. It’s also possible it could be done via extension, though in truth, I didn’t look hard at the options there.
Keep in mind that for most folks, they really will want a limit on the number shown per page- particularly with images, if you have a lot of them, page load will slow down due to factors outside of EE. I personally would limit it to 10-12 thumbs max. This is likely why the issue hasn’t come up before- at least to my knowledge. That said- if two of you are looking to do the same thing, it might be a good idea to put in a feature request for this ability.