Aiming Issues: Advice Needed!

I have given out a lot of parenting tips/advice on this blog. I try to share any information that I have, that may make parenting a bit easier on others. Now I'm asking for help! My son will be three in a few weeks, has been potty trained for about 8 or 9 months, and will be starting preschool in September. Here is my problem: We can not, no matter what we try, get him to hold his penis when he pees. He likes to stand and pee, but he has a strong stream to which his Papa D compared to an unmanned fireman's hose. We have tried everything, any advice we have been given, we have used. No luck!

Here are the things we have tried:
Bribery of toys and a backpack for school
Cheerios for aiming
Leaning over the toilet
Treats (m&ms are his favorite)
Pleading
Discussing how he will need to do it himself in preschool
Threatening (he just laughed at us)
Making him clean the mess
Practicing outside-he loves to pee outside (treat), but still refused to aim

Finally, after a month of cleaning the bathroom top-to-bottom after every bathroom break, I decided that he is not ready to stand and pee. We started having him sit on the toilet, but once again his stream could not be contained! He still peed everywhere, even with a kid's toilet seat with a pee shield (this just made the pee splatter and spray his way). A couple days ago, I started having him sit on the regular toilet seat and just point himself down. This worked.....for a while.
Then today, he was sitting on the toilet, started to pee before aiming, and the pee went everywhere! It sprayed him, the shower, the wall behind the toilet, and flooded the floor. This time he tried to get it under control, but the stream went in-between the toilet seat and the toilet bowl. Once again, I cleaned the bathroom top to bottom.
I now have a 2 month old and cleaning the bathroom several times a day is not really feasible. I'm looking for any advice, any tips or tricks that have worked for others. I'm at a loss, and am worried about how things will go at preschool if we don't figure this out. Thanks!

What it looks/feels like to help Liam pee.