Is there any way to make one property equate to another in the custom properties window?

EX: I want the custom property "Frame Length" to equal the Value of the SolidWorks generated property "LENGTH" in a weldment. Preferrably without using a design table.

I'm trying to work within the bounds of some exisitng templates & overhead...

I posted a similar question in BOM's (with wayyyy more detail) but I wanted to see if a simpler question might get some better results...

Thanks!