No, you can only put a name of a procedure into a button. Even if you need just one primitive to be called from a button (like cg), you need to create a procedure first.
Also, a button can only have one procedure in it, not an instruction made of several commands.
For former MicroWorlds EX users this may look like a limitation, but we made this on purpose. In Lynx, we focus on coding. For clearer structure and easier debugging we wanted all the code to be kept in the same place (Procedures Pane), not distributed among different objects -- turtles and buttons.