Hmm I don't know if it would work, just a thought I had while reading this. But maybe you could just use the vector of the Bmap entity itself then offset the vector by the X and Y values where the pixel would be located (from the origin of the BMAP)? Even rotate the value if need be perhaps... Just an idea.

Edit added image, you would have to know which pixel you wanted for this to work. (if the BMAP were rotated, it would require more calculations)