SN65HVD1782: Voltage tolerance on bus pins

Part Number:SN65HVD1782

Hello,

We would like to be able to disable the driver part of the time and then add an analog signal on bus lines from a DAC IC. This requires tolerance of a differential voltage on the SN65 bus pins. We are however unsure of the max dif level that is tolerated of the IC. Is this be understood as -+30V (differentiel to gnd) or maximum -+7V (differential to gnd) for each pin?

And do you see this as a viable solution?

Thanks for inputs. 

Best, Christian