James,
The answer to your question is yes, although it is not ideal. If you find the side-to-side clearance insufficient, you might be able to pull the dark slide out into the sleeve, which, if it doesn't seal out the light on its own, could be folded over once at the cuff and clipped to do the trick. When flattened, the sleeve is about a foot across, which would accommodate a 5x7 darkslide.
In comparison, there is considerably more room under an 8x10 BLACKJACKET(TM) than the 4x5 and 5x7 models (which are identical save the size of the neck). The default 8x10 model has a clip to restrict the collar size to 32 inches for occasional 4x5 use. If you'd like one made with an additional clip set for 46 inches, it would be a simple task.