Paste the following on to your toolbar (as explained in How to add buttons from this forum to your toolbars):
<?xml version="1.0"?>
<button backcol="none" display="both" label_pos="right" popout="bottom" textcol="none" type="menu">
<label>&Drives</label>
<icon1>#drivebuttons</icon1>
<button display="both" label_pos="right">
<label>Drive Buttons</label>
<icon1>116</icon1>
<function type="normal">
<instruction>Go DRIVEBUTTONS=labels,lettersbeforelabels,hideempty</instruction>
</function>
</button>
</button>
You should then be able to open the menu by pushing Alt-D and scroll through it using the cursor keys.
If you want to use something other than Alt-D, edit the menu item in Customize mode and look at its label, which will be &Drives. The &D part means that Alt-D is the hotkey for it, but if you put the & before another character then you can change the hotkey to something else (although not F1 in this case; you can bind commands to Alt-F1 but not menus).