Dealing with "soft" project time frames

I started working with a local nonprofit client earlier this year who hired me for marketing and PR consulting services. The scope of work for our contract included several items that were within my control to complete, but all of them were predicated on the client's approval to start.

Due to powers beyond my control, several of the items have been delayed by the client more than once. So now the contract is due to expire but the items in it still need to be completed and no discussion for additional compensation has been made so far.

It's never happened to me that projects in a contract couldn't be completed within the designated time frame due to outside factors. I've always been able to work on and complete projects at the same time as being compensated for the work performed.

To make matters a bit more confusing is that fact that I ended up investing many more hours with this client than what I am actually being compensated for due to the amount of hand-holding needed. I did not know this is how they would be as a client going into the contract or I would have approached my pricing structure differently.

So I feel as though the compensation I have received to-date is actually on-par with the work being performed and the time invested in meetings, phone calls and email exchanges, even if it doesn't cover all of the items contained in the contract.

At this point in time I can see no way around it - I'm going to have to finish the remaining items on the client's schedule in early 2012 and not be compensated for my time working on them since the client thinks they've already paid me for the work. I will also need to figure out how and when to cut off the work being performed so it doesn't morph into additional projects outside the scope of work outlined in the contract.

To avoid this happening again, I'm wondering how best to approach future projects where I suspect that the overall time frame might be "soft" so that I am doing the work I am being compensated for at the same time I am being compensated. I'm just not fond of getting paid now for work to be done later. I think it creates a gray area with the client when they are not actively paying you while you are doing work for them. Maybe that's a simpleton's approach but I believe in being paid now for work being done now. Any advice?