Dyamic block Question

Here's what I have:

A dynamic block that, when I stretch it, it automatically arrays at the specified distance. What you're looking at is a platform section view, that has a toggle every 2', but without putting a toggle within 6" of the end of platform. For example, if the platform is 4', there is a toggle at 2', but if the platform is 6'4, there is a toggle at 2', 4', but not 6'. I achieved this by placing the drag point 6" shy of the end of the platform.

What I would like to have:

What I have, with one simple difference. When I grab the drag point, of course, I can type the length that I want. However, right now, when I enter that length, I have to subtract 6" from the length that I actually want, because the drag point is 6" shy of the actual length. I would like to be able to type the full length of the platform instead, but keeping the toggle placement as I have it now, not hitting within 6" of the end.

Can anyone help me with this?

File002.dwg