SSRS 2008 Change Axis Scale Options based on Parameter

I have some data in a chart using SSRS, sometimes we want to see the data on a logarithmic scale - I want to have a parameter that allows me to check this on and off and possibly provide the log base. (I don't want to provide a second graph).

I can't see anywhere to modify this using an expression. Does anyone know how 开发者_JAVA技巧to do this?

It doesn't look like this is currently possible.