I can do it, but I've no idea how I'm doin' it. It just happened one day when I was playin' Marth. Tried t' replicate what I thought was a glitch, and I learned t' mash all the buttons on the right side'a my controller to Glide Toss. I didn't actually know I was Glide Tossin' for... at least a year IIRC. Didn't find it important since I never played characters that can nab items, nor did I often face anyone who used said item-abusin' characters.
It's a dodge cancel. Dodge in the direction you want to slide then jam the C-Stick or your equivalent to a C-Stick in the direction you want to throw said item.
I had to do the battle over again. And this time I took more casualties.
I just encountered the saltiest player I've ever had the pleasure'a vBrawlin' (or so my memory tells me). Ain't got a clue what I did to set 'em off, but he wasn't havin' none'a it. T'was an intermediate Smasher; the kind that's well above n00b tactics, but still has a long ways t' go at applying advanced metagame nonsense t' their play style. Those sorts of players tend t' be the sorest losers from what I've noticed, so maybe he was just a really sore loser.
Would'a stuck 'round and continued my apparent pushin' of his buttons, but lunch > P:M >>>>>>>>>> vBrawl.