I am at the S60 launch here in CA and spoke with Volvo Car USA's main person at the plant. She is aware of this event and are totally on board. They need at least six months to plan, which they should have if this happens next summer.
There is a 1.5 mile driveway in front of the plant and another 3mile road leading to the plant. The driveway will offer great photo ops with the Volvo sign and various flags as back drops. There would be some logistics around hotels in Charleston but there are some that could handle 700 or so attendees, probably more with spouses and families.
We need to nail down a date. The UK record attempt is in March - perhaps some time in June, July or August when kids are out of school.