Yes, this is totally possible in Tableau. It requires some dual-axis tricks to get shapes on some measures but not others. The following post has a link to a workbook where I put a bunch of ideas together: http://community.tableau.com/message/171852
In it I show one version of doing KPIs. In your case, where you're doing a variance calculation, the results of the variance calculation are a continuous variable and Tableau would try to draw one shape for each value. You need to create a bin calculation to take the results of your table calculation to generate one value for each shape you desire. For example:
IF [Sales YoY Growth] < -0.1 THEN
ELSEIF [Sales YoY Growth] > 0.1 THEN
"Not Much Difference"
Then you can put this calculated field on the Shape shelf and you're all set to start formatting. An example workbook showing this is attached.
KPI.twbx.zip 1.1 MB
Jonathan, you are a star. Thanks so much, your solution was exactly what I was looking for.
Have a great day.