Hello,
The short answer is.. no, not currently.
Each sprite image (in SpritePad) can only "have" an overlay, meaning that the current sprite is always treated as an underlay (if only a single layer).
For this reason it is easiest to draw your overlay first, ie. a black hi-res outline, then configure the desired overlay distance, then move to the underlay image, set it's "Has Overlay" checkbox and and colour it in.
From a programming perspective, as the renderer moves through the images it can only (easily) determine if an image *has* an overlay, not if it *is* an overlay.
(Each image contains only a "Has Overlay" flag).
The renderer would have to be made more complex (and slower) to do what you would like and then all of the underlays and overlays would appear the same in the sprite set window (ie. both layers rendered), a bit confusing I think.
The next version will at least have a toggle button to quickly switch between underlay/overlay.