The reason for a tackle is to allow you to easily pull the foot along the boom against the wind load in the sail, not because the foot is hard to stretch out flat.
Also to have more travel, it is much easier to pull the foot another half inch by pulling 4 inch of rope rather then pulling 0.5 inch. Sometimes we have lots of purchase not because we need the force but to allow for very fine control.
Another trick is to lubricate the sail and/or groove with Teflon spray. Or use the old fashioned (and time proven) candle stump method. (I do it once every year). And while you are at it, also lubricate the luff and/or the mast groove. BTW, never use silicon lube spray! Its rubbish!