Hey Hype, i've been using dominoes on mine as well, and found it wasnt as easy as i had planned either. You really need to have the spacing just right. Because if they are too close or too far, they will just push the dominoes and not nock them over.
Their friction needs to be adjusted really well so that they will continue to slide down after they pile up, i ended up lowering my friction to 1.5 and gave them an elasticity of .8, that really helped them behave better. Also i ended up with a higher weight than i would have expected. Take all of these into account, and things will fall (pun intended) into place.
i look forward to seeing more!