There is nothing special in reset circuit design for entering the bootloader using the "V", it's just the RS232 level convertor only for Tx and Rx - you run FlashMagic set to the "V" device, that will start sending "U"s, then you reset the mcu which waits at the beginning for the "U"s and if it sees them it enters the bootloader mode - and that's all. You don't need to fiddle around with /PSEN as it was with the "C" device.
If this procedure is not suitable, e.g. if there is a continuous serial stream on the UART even while resetting is possible in the final application, the bootloader can also be customized if needed, so that it enters the bootlader mode upon a different condition (e.g. some pin set) - but that needs reprogramming the bootloader.
Jan Waclawek