1) Can't outrun him on pace.
2) Can't kick with him off a fast pace.
3) CAN kick with him off a moderate to slow pace.
This is what we are dealing with in a "clean" race. El G showed us #3 is possible if you are reasonably close to him in 5k ability. You also need a miler's raw kicking speed... Bekele is pretty much maxed out at 53ish or so for a last lap, so you've got to be able to hit 52 or lower to have a shot at him, which El G did. Bekele's a great kicker, but not the greatest, and that is his weakness... He was kicking like a madman with his trademark 53 last lap in Athens, but El G mowed him down with his superior SPEED. So, we know Bekele can be beaten by a world record miler in a slower 5k. This means that the odds of beating him "cleanly" are slim to almost none, it took El G to do it, not many of him around. So... Let's get dirty...
Get into the guys head, make yourself visible before the race by being annoying. Get in the way of his strides, brush up against him a bit "accidentally" etc... There are a multitude of options here. Get talking to him when he is trying to focus. Annoy him a bit so that he recognizes you after the race starts, and the real fun begins. First off, if you are of El G's caliber, just follow him around and hope he stupidly relies on a last lap sprint with next to no buildup. Probably won't happen ever again, he learned from Athens.
So... MAKE him run a slow pace. Every time he goes to start his finishing drive, PASS him and instead of plunking back down into lane 1 on the rail, run really close to the line that starts lane 2. JUST ENOUGH TO MAKE HIM THINK HE CAN SQUEEZE BY YOU ON THE INSIDE. Tighten it up in the turns a bit though so you're not running too much extra distance. Give him a good look at the inside down the straights. If he bites, close the door and force him onto the brakes or off the track, being as subtle as possible about it. This is aggravating. DO NOT LET HIM PASS YOU ON THE STRAIGHTS. Make him do it in the turns around the outside for the extra distance, and this will aggravate him to no end. Easier said than done, but when he gets by you (eventually he will), try to pass him back (brushing shoulders as you go by), and just repeat the process, hoping it's taking more out of him than you (probably not, but it's worth a shot, the guy can't be beat otherwise). This just might tax him enough where you will have more kick than him on the last lap. You basically have to completely f*** up anything he has planned for, and I think this may do it. You obviously have to be reasonably close to him in 5k ability, and it also helps to have more kicking speed. Regardless, it will take a very talented runner to make even this oddball strategy work. This of course doesn't take into account the other runners, one of whom may just leave you two to your game and run off into the sunset... You can only block one person at any time. Odds of being successful against Bekele: Reasonable. Odds of being successful against Bekele, and all the other runners in the field: Not so reasonable. Obviously this is a one-time thing, reserved for the one Olympic final you intend to beat him.