I would get your staff qualified in a recognised ladder safety certification. Iosh or similar. Then provide them with the correct ladder safety kit such as laddermate and a decent stand off.Have a tight risk assessment drawn up and get them to sign it. I do these jobs on my own and feel pretty safe but I don't take risks and neither should your guys. I have turned jobs down because of safety reasons.
That still wouldnt cut it with h&s smurf. If u being strict by the rules of an employer Under no circumstances would a single man operator be ok to carry out that job. I recently passed me accreditations for safecontractor & chas and the stuff they bark on about is unreal.