I've had a skim, but haven't seen this mentioned yet. Quickly hacked together but seems to work, regardless of whether the scroll bar is set to show or not:
tell application "System Events"
tell process "Keyboard Maestro"
tell window 1
tell group 6
tell splitter group 1
tell scroll area 3
tell scroll bar 1
set value to 0 -- moves thumb to top
-- set value to 1 --moves thumb to bottom
end tell
end tell
end tell
end tell
end tell
end tell
end tell
Whack it in an "Execute an AppleScript" action, comment in/out the set value... statements as appropriate, set a hot key -- and Bob's your mother's brother.