I disagree with Revitaoist to a large extent (SketchUp can create amazing presentations, just look on SketchUcation's gallery; Revit's strength is not rendering), but agree that Revit can be used very effectively as a conceptual design tool. Does your firm's website show any of the presentation material you typically use? Could you post something that is typical because how much you have to change in your process depends on what you hope to produce.
I have attached some screen grabs of a early stage client presentation. its an animated flythrough that was quickly done in sketchup. We are not interested in photo realistic renders or animations. If we need to do those we would outsource them. To be honest most of the renders on the Revitcity gallery were very cheesy and be stuff we would never do
I think the primary thing necessary to convince people of it's usefulness in the early stages is the long-term pay-off. You are going to waste time transitioning your design from SketchUp/ACAD to Revit if you use both sets of tools. Why model something twice, right?
If you already see the benefit later in the project, then how do you make people start it early. Area calcs are a huge one. If you already use 3ds, there is an excellent workflow between Revit and 3ds. If you ever do or have a desire to do preliminary energy analysis, there are some built-in tools that could be quite nice. Finally, if you do anything with facade systems more than just standard curtainwalls, you should check out the conceptual mass and adaptive component tools. Here's something cool that you can't do it SketchUp:
Louvers that know their orientation.
Beyond that, it's being in it for the long-haul. Why throw away your schematic model and start again when you could already be there (and more)? I think using it on a project as a case study is a good way to start, then giving a very well thought-out presentation of a successful project in YOUR office might help.