Thanks a lot, it worked!
I'd seen the attribute in the XML sheet, but couldn't make it work because it doesn't say you need a "pointers" element wrapping the "pointer" elements (in case someone runs into the same problem as me).
The other widgets I'm using are the bullet charts, that don't seem to accept the "pointers" element. I guess this means it's not possible to customize the toolText in these charts, is it?
Hope you can answer the question. Thanks for your support.