Change search function on Joomla site

I need my filter work in a slight different way in the SOBI2: Right now, when i mark two or more fields/categories - all entries connected to either one of the two will show. Instead i need it to show all entries that are connected to ALL marked categories. So when i for instance mark 3 categories: Carpenter, Welder and Driver's licence - i will see only workers/entries that are all 3 - so i can easily find the Carpenter that also is a welder with a driver's license. Note that this filter is custom made. (see screen dump)