Help with early access and contract clauses

Hi all,

I wasn't really sure where to post this, so I hope it's in the right place.

I'd really appreciate some feedback on our current situation.  Basically, we're looking at buying a unit and doing a quick'n'dirty cleanup, then renting (your basic buy and hold strategy).  However, I'm interested in negotiating early access before settlement, which would obviously give us more time to sort it out prior to having to make mortgage repayments. 

My main question is this: what are some suitable clauses to include in the Offer & Acceptance contract?  For example, I'm aware that insurance is an issue, and that there's a way in which you can register as an interested party, but am not sure of the specifics. 

Any info (general or specific) would be very very welcome!

The other question I have is, what are some good negotiating tactics to use with the seller, to make the idea of early entry appealing to them? (Currently the unit is tenanted on a periodic lease arrangement, so we wouldn't be disturbing the owner if we did get early access.)

Thanks all for reading this far!!

Regards
Petrona