Hi,
I assume the reason it's disabled is that each spoke on a radar chart is
a x axis for a data point and to add spokes between data points would be
confusing.
Two possible way to get the chart you want either add a second data
series to the radar. Plot a point for each angle, so 360 points, where
all values are zero except for those angles where a spoke is required.
For them set the value to the maximum scale value. You will need to fix
the maximum scale value in order to stop the chart from auto adjusting
its scale.
The other way is to construct the whole chart yourself using a xy
scatter and a collection of data points to plot the spokes, gridlines, X
axis gridlines and actual data plot. Quite a bit of work but not impossible.
Cheers
Andy