Help needed for Pin assignments using Quartus II

I am designing using Quartus II and SOPC builder. I am sharing the address for Flash memory and tristate bridge and the problem is the tristate bridge address pins are configured as output pins and I am unable to allocate address for the tristate bridge as the address pins are already allocated for the flash memory address. But still in the Tristate bridge megafunction, I have chosen the option to share address with flash memory. I have checked in the Nios II standard project example where they have allocated the same address pins for both tristate bridge and the flash memory. The only difference they have made from my design is that they have assigned the pins as unknown. Is there any concept like if the pins are not registered, then 2 or more pins can have the same pin location. And if that is the case, could someone tell me how do I change the pin assignment to unknown? I have already tried but it works only with single pins not for address or data bus...