Change at work. Leave Jacket & shoes there, take in two pairs tousers on Monday, take in a shirt & tie each day. Wear Aerostich if going for an meeting/interview somewhere not too far (an hour or so), otherwise I just carry clothes and find a toilet to change in when I arrive, almost everywhere has a disabled toilet that provides ample room to change easily, and it is often near the main entrance (in, change, take kit out to bike and stick it in the Jesses).
I leave the pillion seat off, I have a Magellan 'Suit Roll Carrier', basically a suit carrier that rolls around a central tube that holds shoes, belts etc. Its waterproof, works, and fits nicely across the tool rack/ panniers (once the pillion seat is removed).
Lucky enough to have a shower at work, although I rarely get to use it; Too many sweaty cyclists in the queue.