Arria V SX Boundary Scan Mode Power dissipation

If you will power on the device, hold it in reset, and perform boundary scan before allowing it to begin configuration, then the power should be very low. Unfortunately, this power is not specified, but will not exceed the static power of an empty device. So my suggestion is to use the EPE to model the device with the HPS off and no resources instantiated (remember to use MAX power model), and specify the heat sink as None, and see what you get.
Let me know if you have questions :-).