What version of FrameMaker are you running? FM 12 has a customizable Quick Element Toolbar that may be what you want. See:
for information on both using it and customizing it.
Thankyou Lynne, but it is Framemaker 11.
You might want to have a look at Klaus Daube's work on enhancing the toolbars at http://daube.ch/docu/fmaker55.html and also his write up on more details of customizing FM in this pdf: http://daube.ch/docu/files/etb-customising-fm.pdf
The work is mainly for unstructured FM, but it can also be applied to structured FM toolbars and I believe that you can use combined fcodes in some some command actions (there are some keyboard shortcuts that work this way).
I managed to get it going by calling Extendscript registered commands....