Yes there is, with limitations, and recommend against it.
You said that you use the noreg, which what you would need. However, the only thing you should need to change is is the img=down to img=up for each individual image. I don’t have the commands in front of me, but that should be all that’s needed.
HOWEVER, there is a fail-safe measure that’s removed when uploading the image. When you upload the image the normal way, it writes the image to a temporary file until it’s completed, then writes it to the original image. If you upload an image with noreg, it’ll directly overwrite the image and not worry about making a temporary file first. What you would need to be careful with is that if anyone tries to image a computer with the image you are uploading with this method, they will push down a corrupt image since it’s currently being pushed.
I’ve personally never tried it, but you should be able to set the image similar to pushing it to a machine, but instead of down, put it to up. Of course, you’ll probably need to create the image template first in the FOG web interface. If you skip this step, it might still work, it might just not show up as a selectable image.