You can use DRAWING_SCALE_FACTOR as a paretmer in the model that the drawing will automatically pick up on. That is a TON easier then trying to do it via J-Link. Assuming you are completely generating a model from scratch with J-Link (which I doubt) if you could append the relations via J-Link to include your calculated value, or relations based on other model dimensions/parameters or what ever.
I'm not sure what you're thinking of here, Dave, with drawing_scale_factor. It's not a config option, not even a hidden one, at least not according to Olaf Corten and proesite.com. Maybe a plain old parameter? Holding some value that you'd use how? Or maybe you're thinking of the one I mentioned in my earlier post, default_draw_scale which, when set to NO, does the proportional scaling we see in most detail drawings.
But, you're right, there're probably easier ways to do this with the internal parameters, maybe some relations, etc. Still, most automated ways are at least a takeoff on manual ways, repeating their mechanics quickly or developing an algorythm that captures the essence of what's going on. Since this whole thing of scaling really boils down to numbers, it could be an iteresting mathematical puzzle: dimensions of hte part in a top and front view vs the space available on a drawing format. You'd have to make some allowances for borders around views, space for dimensions and other annotations, say 20%, but that still comes out to be some ratio or "scaling factor". It might even provide the information needed to decide the optimum format/paper size to use.
Anyway, the chief thing missing (can you get this with jlink, Prabhu?) is the model size. There's some teaser functionality in Pro/e called 'Info>Model Size' which gets you some virtually useless 'diagonal' because, for any length diagonal, there are a nearly infinte number of boxes that can have that diagonal. But, what you need, to determine the needed space, at a certain scale and a certain view, is HxWxL numbers. If you can write a jlink app to capture this information, you'll have x, y, z numbers to evaluate for the drawing space available for any given format and drawing size.