I'm not sure anybody has determined whether or not the virus would be present in semen and even if the beneficiary of your attention doesn't cum, he's likely to leak.
When a cough occurs, although most of it stays in droplets some gets aerosolized and still could waft through the opening.
Although you could disinfect his side of the cubicle between uses, I personally would not risk it.
(And you'd have to santize doorhandles, tabletops along the way ...).