There are these, not tested though, but, it maybe what you are looking for.
Then the call would be to the WS_EX set for nIndex (-20) and set WS_EX_TRANSPARENT (32), you may need to also OR the other WS_EX values to achieve the result required, but I hope this sets you in the right direction.
When I was messing around with this before it did work as expected, but for the life of me can't remember all the flags I included. :)
.lib user32.dll SetWindowLong% (hWnd%,nIndex%,Value%) : "SetWindowLongA"
Then the call would be to the WS_EX set for nIndex (-20) and set WS_EX_TRANSPARENT (32), you may need to also OR the other WS_EX values to achieve the result required, but I hope this sets you in the right direction.
When I was messing around with this before it did work as expected, but for the life of me can't remember all the flags I included. :)