Implementing B210 GPIO ATR for both channels

Question

I am planning to use the GPIO ATR on a B210 as a PTT signal. Both channels will be used on the B210. Currently, GPIO ATR can't be switched from channel A to channel B on the B210 due to the function not being implemented in UHD, from EttusResearch/uhd/host/lib/usrp/multi_usrp.cpp

void set_gpio_src(
const std::string&, const std::vector<std::string>&, const size_t) override
{
throw uhd::not_implemented_error(
"set_gpio_src() not implemented for this motherboard!");
}

Could this functionality be implemented with a script that directly accesses the ATR or tx/rx status registers? Or would I need to build custom firmware and modify the UHD drivers? Are there any good resources or tutorials for how to do either of these things?