You don't absolutely need PSEN and RESET under PC control. You can control those lines yourself.

If you need automatic, rapid reloading of code, get your project working to accept characters from the UART. Designate a special character sequence (such as "U") to initiate jumping directly to the bootcode using the "__api_start_bootloader" command which is in one of the clunky libraries available from ATMEL. I'm not sure if I used this method successfully but I did put it in my code.