To do this you'll need to have the Dominate skill, the Retrain Powers and Advanced Training upgrades and tons of Element Zero. You can get the Dominate Skill by recruiting Morinth (Samara's daughter), which means you have to sacrifice Samara in her own loyalty mission. A list of planets with Element Zero can be found below. First, purchase Advanced Training and choose Dominate. This will land you a bonus skill point, which you can use by instituting the Retrain Powers upgrade. Repeat this process for additional skill points -- one at a time!

Another technique by drenthez: This cheat works best when you have at least 10 available points. Simultaneously press X and A when choosing the fourth rank of an ability. This bumps up an ability to the next rank (fourth), but keeps any points spent to get there. For example: if you decide to do this when a rank is at level three, then it would cost 4 points which you would then be given back. When you do this using all 10 points on an ability, you get all of them back. Free Skill Points!

And finally, an addition by Dale Dearnley: If you do not press the X and A at the same time you can "Back" out and "Undo Talent Points". Go to the "Retrain Powers" menu. Retain and max out all powers using the above X and A cheat. Then go to the "Advanced Training" menu and buy a new power. It seems that a character can only have seven total powers at one time but you can buy the same power more than once so that a new one over rides an old one. Go back to the "Retrain Powers" menu and retrain all using the above X and A cheat, again. You will receive at least 50 extra Skill Points. If you up your skills in the "Squad" menu you will NOT get the extra Skill Points. This process can be repeated for more Skill Points.