Offer on multiple houses with separate closing dates

[Cortney Arenstein]

Asking for an agent friend: 

Repping the buyer, buyer wants to offer on 5 houses, all of which currently have tenants. 

Tenants' leases each end on different dates. 

Buyer wants to wait to close until AFTER each tenant's lease is over and they have vacated. (Got burned in the past) 

No lender involved--all cash offer. 

SO...agent wants to know if she can write ONE offer for all these houses with separate closing dates. I said "NAH." Separate closing dates means separate contracts, because title will be involved multiple times, etc. BUT, I can't find any actual RULE that says this--and i assume an attorney could draft an offer contract like this. (since the agent can't alter the promulgated contract forms) 

ANyone have a similar experience? Thoughts?