Before I invest work in this, a few questions: Do you need the prototyping pads (circled in red in this image?)
They are a lot of work to add and their position isn’t clear. Next issue is that the part will look like the image (i.e. no breadboard) as breadboards aren’t compatible within parts (the internals are different). The same effect can be had (with some inconvenience) by dragging a suitable breadboard over the part like this using a Uno as an example:
The downside is that unless you select both with a select rectangle they won’t move together. Staring from here (with some wires attached to the breadboard)
if I move the Uno the breadboard remains in place (you can then move the breadboard back to where it was though)
If this is acceptable I can make a part for the shield.
Peter