The "Scale to Linear Dimension" command:
This command scales an object by clicking on the start point and end point of a reference line then, a dialog will ask for the length of the reference line.  The object will then be scaled (from the line's starting point) to fit the reference line to to the new length.

NOTE:  This command was designed to be used on bitmap objects but should work on others as well.  Rotated bitmap objects will not scale in vectorworks with this command - These objects can be rotated back to "0" in the Object Info Palette to make this command work on them.

WARNING:  This command has not been extensively tested so use at your own risk.

OPEN SOURCE:  This command is open source.  If you find ways to improve it, please send me the updated command.  This will allow me to post improved versions of it on our website.