I think step one is killing Washington. Everyone knew he was going to be the first President, and the system was set up with that in mind. Without Washington, the Presidency could have - I think almost certainly would have - been set up as a much weaker office. There was also a current of thought at the time that the Presidency might be a lifelong office. Let's combine those and additionally fulfill a longtime AH.com wish, putting Ben Franklin in as the first President. Franklin was quite old at this time, but that's not a problem. Quite the opposite in fact: Everyone trusts Franklin not to go all Caesar on them. So you already have a weak presidency, and its first few years will be filled by an old man with neither much of a desire nor ability to accrue a lot of power. From there, have things muddle along a few years until someone in the House sees the potential of the Speaker's role - Madison and/or Clay, for instance. There's something for you, then: A weak presidency seen as a sinecure for national heroes and prominent men past their sell-by date, and a commanding speaker in charge of a more powerful than OTL House.