I’m not totally sure on that one.
One thing to note about the slider is that URL’s are saved at the time you save the slider so they don’t need to be queried every time your site loads. So, when a slider is saved, the URL’s to the images at that time are what’s saved for the entire slider. Then those images URL’s get used every time the site loads.
As a workaround, would it be possible to turn off forcing the admin to SSL temporarily, just to save the slider one time? I’m not really sure what else you could do.