After a long hiatus, spent a few hours adding two sliders for the start and end angles of the clothoid.
It only took a few minutes to add the sliders, but a lot longer to get everything working more or less properly,
due to limited programming skills and limited understanding.
Much of the code is in the htm file, as per Michaels post.

The MoI3 version of Blend command was used for the basic pattern, but had to modify it per Michaels help of many months ago, since
the sliders do not have a "clothoid factory" to work with. The sliders work "better" in Blend command, (in my opinion).

Is there some way to make the clothoid sliders update interactively, not just when the mouse button is released?

Angles can also be typed into the boxes.

The MoI3 version does not quite work in MoI2. MoI2 hangs up for awhile, but then permits exit from MoI2.
The MoI2 version of Blend appears to have a different line in the slider code.
Including this difference allowed a version that works in MoI2, and it also worked in MoI3.

Attached a MoI3 version, and also a MoI2 version, both with limited testing

Edit August 2, 2013...See August2 post for updated onmousemovevaluechange sliders for MoI3August1Beta.