Yes - you can do this by defining a press sheet size that uses a variable for one of both dimensions. When you define the width and height in FFCore v4.0.3.0 and later you will have the option to use a variable instead of a fixed value
The first variable in the menu is the Stock Height or Width which can be defined in one of the following ways:
Alternatively, you can define a numeric custom MAX variable and use that when defining the press sheet size