Let me see if I got this straight…

Let's say I have a Goblin Test Pilot and a Suppression Field. I activate Goblin Test Pilot, or rather I begin the process of activating its ability, the random target is chosen and when I reach the point where I have to pay the costs I decline to activate any mana abilities, which means I can't pay the extra two mana. Now CR 602.2+717 kicks in and rewinds the game to point just before I put the ability on the stack. I repeat the activation, only this time I'm luckier and a “better” random target is selected, so I chose to pay the additional 2 mana by tapping some lands.

Essentially, adding a mana payment to the Pilots ability will allow me to select any target I want with a bit of patience (count all legal target, declare the shortcut, and roll a die until I hit the right number).

I'm pretty sure this works, but it is a sufficiently weird interaction that I thought I'd better get a confirmation.

Edited Scott Marshall (May 14, 2013 05:23:38 PM)

While the game rules may support that, I have yet to find a judge (in my very informal survey) who wouldn't DQ you for Cheating. After all, you're intentionally taking an illegal action to gain an advantage - unless you happen to hit on the first try, then this isn't relevant at all.

Even if you try this at your kitchen table, most judges I've spoken with agree you're in line for a “hard slap upside the head”. (That phrase might not be part of policy…)