I’ve made some honest attempts to grind and during the week of Thanksgiving (my break) I made a funbox complete with 8 foot angle iron. I could usually get a few inches, but then my pedal pins would dig in to the wood and I would go flying. Is the goal to slide only on the pedal? I hope so, because my bearing holder is missing a lot of paint now. 
You will slide a lot better if you don’t grind on the bearing house.
You will also slide better if you tried, removing the pins in your pedals, getting plastic pedals, making/buying grind plates, or just wearing down the pins in your pedals
my personal preference is grind plates on metal bmx type pedals.
yeah you need to get rid of/cover your pins. That is obviously what is causing the problem, I just removed what pins I could from my right (grinding side) pedal and grinded the rest away with a bench grinder, alternatively you could build grind plates, which are pretty simple to make. Instructions on how to make them are on www.unicycle.2ya.com on the 'Street Skills" page. Hope this helps. Oh and I grind on my pedal and crank, that is what i aim for anway, sometimes I think i end out grinding on my bearing housing aswell, but this seems to make no difference.