If you are building your own firmware...
For example for Revo: in flight/targets/boards/revolution/firmware/pios_board.c
It might be (I have not verified it) as simple as changing this around line 865:
if (hwsettings_mainport != HWSETTINGS_RM_MAINPORT_SBUS) {
GPIO_Init(pios_sbus_cfg.inv.gpio, &pios_sbus_cfg.inv.init);
GPIO_WriteBit(pios_sbus_cfg.inv.gpio, pios_sbus_cfg.inv.init.GPIO_Pin, pios_sbus_cfg.gpio_inv_disable);
}
to this:
// if (hwsettings_mainport != HWSETTINGS_RM_MAINPORT_SBUS) {
GPIO_Init(pios_sbus_cfg.inv.gpio, &pios_sbus_cfg.inv.init);
GPIO_WriteBit(pios_sbus_cfg.inv.gpio, pios_sbus_cfg.inv.init.GPIO_Pin, pios_sbus_cfg.gpio_inv_disable);
// }
to make a version of firmware that turns off the Sbus inverter.