Phil
The old "Fast Track" system did this. I think you may know a little as you asked about packages. its a full on computer presentation. they used to offer free room. then when they had done the clean sat down and gave the presentation for a maintenance package. it worked, but you have to be the right type of person to do it.
its like the get free Disney tickets. where you had to sit thought a time share sales pitch to get them. the method works or they would not be able to give you those passes. sure your price has to high to pay for your effort, but as I said its does work for carpet cleaning.
If you do it I would say dont use the word free but change it for sample clean. people will be less fearful. I do think if you really want to go the full house way then this is the only way you will sell it. The offer can be anything really just has to be risk free and irresistible for the prospect. The trick is that your not sell the full house your selling the presentation, just make sure they know in a round about way this is the case. saying something like "let us show you how you can keep all you carpets in your home clean all year round" So you give the sample clean, this shows how great you are, then you show them the second part with the presentation on how they can keep them clean all year round with the Maintenace clean for a few pounds a month.
Maintenace cleaning are a great way to get regular turnover. you get monthly payments into your bank. you build up a real business this way. one that you can sell.
Good luck
Ian Harper