Create stacked bar charts with percentage of total which allows filtering

Hi,

I'm visualising survey data. I would like to create stacked barcharts for a number of different questions in one graph, showing the percentage of total rather than the absolute number of respondents who chose each answer (see screenshot). But now I also want to be able to use a filter (i.e. only show some of the answers) without changing the percentages.

I have found how to keep percentages when filtering using level of detail calculations, but those involve creating calculated fields and then I'm no longer able to pivot so I can show the barcharts for multiple questions in one graph.

Any thoughts?

All help is much appreciated, this is driving me slightly crazy :)