Use USB-to-parallel cable as UART?
The parallel port connector has pins designated like this: -



And, here's an example of where D2 is used for driving a BJT: -



This basically informs us that the data lines can generally be used as IO lines providing the host has the software to support this. This can lend itself to a form of serial comms (similar to UART) but it will be totally reliant on dedicated software loops reading the data pins. In other words, it doesn't have the specific hardware chips to inform the host that a new byte has arrived and that byte has no detectable errors and all the other bells and whistles you get with those specific UART chips.