A neat trick in Simplify3D is that you can, in instances like the one you've described, use the virtual bed surface as a cutting plane.
Double click your model to open the model settings panel for your selected part and lower the Z position 152mm. So if it currently reads 0 for Z you would change it to -152.
Here is a video on using the model settings panel:
https://www.youtube.com/watch?v=i5rLVYpeoXU
"A bird does not sing because it has an answer. It sings because it has a song."