Technically auto-canceled dairs are possible without tap jump but requires godlike fingerspeed and timing to do consistently. Stick with tap jump IMO.
Double-fsmash... well it's hardly DOUBLED but it does give it a bit of a boost:
Increasing the Range of Falcon's Forward Smash
*Discovered by T0MMY; notified by the_yoshinator & k4polo
You can increase the range of Falcon's forward smash by starting to dash in the opposite direction you intend to hit in, then immediately hitting the c-stick towards your target. What will happen is Falcon does a little jump forward as he smashes, increasing it's range further than a standing fsmash.
Alternate Method: (Discovered by domiNate) Essentially, what you do is tilt the control forward slightly so you do the first step of Falcon's walking animation (not dashing), then you proceed to hit back on the control stick and forward on the c-stick for an even longer extension on Falcon's fsmash. Takes slightly longer to execute though.