hmmm ... what about using some sort of wrapping paper ... there's lots out therre with grids printed on the back for easy cutting ... and laying out the pattern pieces on the back ... use a ruler to measure out however many inches you need to enlarge it, move over a few inches, do the same ... continue all the way around and then connect the dots?

Or, I have a friend who's a magnificent seamstress, I could try asking her ...