Should be easily possible, both are just function calls. But consider the downside. I used to frequent a (non *-Nuke) site until they added this feature, using the FCKeditor, which was displayed at the foot of every forum page. The forums became very slow and unresponive to use, due to the large amount of date, button images, scripts, formatting, etc. being downloaded for every page.
Perhaps make it a User Preference switch?
The current set up is optimal for those of us not on a fast connection, 'cos if you click Preview at any point in the typing, you get the full screen to add the formatting.