Unfortunately, if you look at www.hmrc.gov.uk/manuals/sdltmanual/SDLTM00365.htm you can see that HMRC will not accept your 'dual use' loophole. Even if you would find an acceptable use for part of the property that would enable it to be classified as non-residential, the value of the remaining part of the house that is residential would still be liable to stamp duty land tax at residential rates - see www.hmrc.gov.uk/manuals/sdltmanual/SDLTM00370.htm.