How can I view a minspantree with meaningful edge lengths

I am using a biograph object to view a min spanning tree. Is there any way to pre-specify the location of the nodes? In my case their actual position is important, and all of the layout tools optimize position to decrease clutter. I don't want them all spread out arbitrarily.

Or, even better, is there a way to incorporate edge values into any of the layout engines? I'd like the length of an edge to be proportional to its value.

Basically I want a layout that you might get from the function mdscale, but constrained by the minimal spanning tree that was already found, and (least importantly), any remaining non-uniqueness to be tweaked for visual clarity.

I still want the nice display of the node labels and connecting edges though. Is there a way to do this?

thanks!