Yes, and it's quite complicated. Do you have the batch analysis for your primary pale malt? You absolutely need this in order to begin.
Do you know the difference between Real Degree of Fermentation and Apparent Degree of Fermentation? Do you know how your yeast, your brewery's fermentation profile, and brewhouse characteristics impact RDF and ADF?
I can't speak for the software designers, but I suspect that the sheer complication of figuring your desired number has a great effect. Basically, the projected FG is based on a ballpark PPG from the grist, calculated through the average attenuation of the yeast strain chosen. It's hard for the software to know the amounts of unfermentables in your wort without your input, and it's hard for you to figure those numbers without laboratory analysis.
What you're asking for is basically impossible to do on the homebrew level. It requires reduction of variables to an almost ridiculous extent, best done in a well-equipped commercial brewery brewing the same batch over and over.
I can try and gin up an approximation, but it's going to be fairly useless, I'm afraid.
Sorry I can't be more helpful!