Plotchart - t-axis labels

I'm trying to plot a set of timed values using Plotchart::createTXPlot.
My first vaguely successful attempt leads to unreadable labels on the (horizontal) t-axis because the date/times overlap each other. I'd like to specify that the labels be displayed vertically, which seems a fairly good and obvious solution but I can't see a way to do this easily using Plotchart commands.
I have discovered by experiment that the labels are specified by canvas items with the tag "taxis", so I can rotate the items with code like this:
foreach item [$canvas find withtag taxis] {
     if {[$canvas type $item] eq "text"} {
         $canvas itemconfigure $item -angle 270 -anchor e
     }
}
but since this isn't documented, I fear it may change in a future version of Plotchart.
I'm also having a bit of trouble getting the canvas to scroll properly which I haven't yet worked out properly.
Is there a better, preferrably a "supported" way to do this?
Thanks