repeat delay for (lesstif) toolkit scrollbar arrows

[Marshall, Simon]

I hesitate in asking this in case I've missed something in the manual...
I use LessTif, which has nice scrollbar arrows to scroll up/down by
individual lines.
However, if I hold mouse-1 on an arrow, the "repeat time" of events that
Emacs sees and calls scroll-bar-toolkit-scroll is too long and scrolling
too slow for me.

It feels like there should be an Emacs variable to control it (like
mouse-scroll-delay, but that seems to be for dragging within a window
only).
Perhaps it is something defined by the toolkit and beyond the reach of
Emacs to control?
Or something defined by the windowing system (I use CDE, but none of the
mouse parameters have any effect)?

Any pointers?