I'd say it is worth a try. Summertime can be harder to get an actual jumpseater, but in most cases this time of year we don't have major weight restriction issues. I have had full boats with someone in the jump. It can be done.
All that said there is a possibility that you could still have some issues if the particular plane has a heavier than average empty weight, and if the bags happen to be extra numerous/heavy on that flight.