[RPG] How to you force an opponent to provoke an opportunity attack

From the DMG/Compendium, the important part for your question:

Forced Movement and Terrain

Difficult Terrain: Forced movement isn’t hindered by difficult terrain.

Blocking Terrain: Forced movement can’t move a creature through blocking terrain (page 61). Every square along the path must be a space the creature could normally occupy.

Challenging Terrain: Forced movement can make some powers more effective or hinder them, depending on the specific challenging terrain. The DM can require the target of forced movement to make a check as if it were moving voluntarily across the terrain, with the same consequence for failure.

Hindering Terrain: Forced movement can force targets into hindering terrain. Targets forced into hindering terrain receive a saving throw immediately before entering the unsafe square they are forced into. Success leaves the target prone at the edge of the square before entering the unsafe square. If the power that forced the target to move allows the creature that used the power to follow the target into the square that the target would have left, the creature can’t enter the square where the target has fallen prone. If forced movement pushes a Large or larger creature over an edge, the creature doesn’t fall until its entire space is over the edge. On the creature’s next turn, it must either move to a space it can occupy or use a move action to squeeze into the smaller space at the edge of the precipice.

A DM can allow a power that pushes a target more than 1 square to carry the target completely over hindering terrain.

Published in Dungeon Master's Guide.

And from the DnD FAQ ( http://wizards.custhelp.com/cgi-bin/wizards.cfg/php/enduser/std_adp.php?p_faqid=1396 ):

Are zones that deal damage (like the Wizard power Stinking Cloud) considered ‘hindering terrain’? Can I make a save to fall prone and avoid being forced into one?

No, zones are not considered hindering terrain. Hindering terrain refers to more permanent features like pits, cliffs or pools of lava.

The resultant answer: For zones, base DnD rules do not give a saving throw to avoid being put into the fire. For pools of acid, you are given a saving throw to catch yourself before it and fall prone.

The Mechanics of Whirlwind Kick's Movement Technique

Effect: You fly your speed. The first square of this movement doesn’t provoke opportunity attacks.

Powers in 4e do what they say, nothing more nothing less. Thus you are free from provoking only for the first square of movement.

How to use whirlwind kick and avoid provoking

As you say, against one enemy you can use that first square to move diagonally up and back to leave their range and then fly where you want to go from there.If you have more enemies near you such as 2 flanking, the 1 square still help to limit it to only one opp attack vs multiple. Similarly, if you have 3 enemies adjacent and they are spaced out evenly there should still be 1 square that only exposes you to one opp attack.

Fluff has no bearing on mechanics

Fluff vs. crunch. Crunch are the rules, the parts of the power card that refer to the rules and the mechanics of the game. Fluff is any part of the powercard that is not crunch: the name of the power and the description of the power.

The descriptions of powers & items in 4e are simply that; no more, no less. The descriptions/flavor text/fluff printed on power cards has zero bearing on rules. Its there to make the power sound more fun, spice up the game, and/or help you visualize what the power is doing better.