"springboarding" a short-stack

[Big Limpin']

You know the situation. You've got the goods (preflop, on the flop, later streets, whatever)

You are fairly sure this shortstack guy is not going to be folding. Multi-way pot.

You bet just under what s/s has, expecting him to bump it up a little as he pushes. You can then thunder overtop. Forcing other healty stacks to either drop some dead money into the pot (90% of the s/s, usually), or have to call TWO big bets from you (the second being a push, usually) without them ever having raised.

Some sites let you do this. Some don't. I am aware that its not legal raise normally, but if your chosen site lets you do this.....

Is it unethical?