You CAN sort of fudge it... make a separate SKP file containing a dimension 1" long and 1" offset. Then in code load it as a component into your SKP. Add an instance at a point and scale it in the X to match the length to another point and in the Y for the offset needed. You also need to transform-rotate it so that it aligns with the vector of the two points etc... When done you can explode the dim-component instance back into a plain dimension. An dims added this way will ever be linked to an edge or vertex as in a manually added one... You could perhaps include a 1" long edge in the dim-component that the dim refers to... and if that then replaced the original line below it when exploded it might keep some linking ? It's better than nothing... but only just...