Clive
Regardless of the number of years or experience in the business, there will always be the odd job where we will be unable to acheive the results we would like without there being a problem or two.
Now, this does not have to be down to our lack of knowledge or know how. If as you say, the carpet is impractical for the environment it is in, and you have told them so, then in my opinion you are being professional in bringing this to their attention and the risks involved in maintaining the carpet. The owners have to take some resposibility here and in particular taking into consideration past history.
Now, how do we solve the problem?
As you state that any overall deep clean using HWE, whether portable or TM may result in shrinkage then a LM system is the only option to avoid such pitfalls. You also state that food and grease stains are already evident but hopefully not too extensive being only recently laid. Personally Clive, I would take in a small spotting machine to remove localised food/beverage stains, but then LM the remainder of the carpet and use dryers. If the staining is too extensive for a spotting machine I would recommend overall LM cleaning, possibly every 2-3 weeks until a satisfactory result is acheived. This may sound over the top, but unless the owners want to accept unsightly shrinkage on a relatively new carpet I feel they have no option. If they agree I believe thereafter, you will need to clean it on a monthly basis using LM.
Some years ago I had a similar problem in the centre of Birmingham and the owners agreed for us to clean it on a weekly basis to avoid any such problems and so it could well work for you.
Regards
Gordon