I would suggest calling and speaking to the Director of Sales. Not sure if Execustay properties have someone in that position, but there should at least be a Marriott person nearby who covers sales for several properties.

In this economy, any property would love to have that many guaranteed room nights, so I'd definitely try to negotiate a deal. Never hurts to ask.

By the way, in some states anything over a 30 day stay is considered a "lease" so you may be exempt from the sales tax and perhaps some other ones too.