Kate Moirfrom Xara opened my eyes on this one.
To create truly interactive gradient (fountain) fills, create a Linear fill (select the Fill Tool then select Linear from the Fill Type drop down list on the Infobar). With the Fill Tool cursor drag the end of the fill path then tap the Tab key on your keyboard. The fill will now follow the cursor as you drag. The fill path arrow will only be visible if you pause.
If you don’t like this method, ”Some love it, some hate it!”, Kate tells me, hold down the Tab key and drag the fill path arrow and you’re back to the default method.