The only hint I can see is part 3.6.3 - 'advanced shape properties'. It says there is a 'visibility expression' for terminals, which define whether a certain terminal is visible or not. This means you would need a component property for the number of terminals needed, and then have for each terminal a test whether it is included or not.
You may want to look into the CyControlReg_v1_70 folder of your Creator installation - it contains the verilog code for the control reg, which shows how to handle a variable number of terminals. Judging from what I can read in CyControlReg_v1_70.cysym, it works as described above (with the addition of checking for the need to display as a bus).
Oh, make that 'part 3.6.2' - stupid keyboard :)