Hey There,
Do you mean an AppleScript choose-from dialog?
The way to handle that is to make sure Omnifocus is frontmost and make sure the choose-from is wrapped in a tell application "Omnifocus" block.
set myChooseFromList to {"one", "two", "three", "four", "five", "six"}
tell application "Omnifocus"
set myChoice to choose from list myChooseFromList with title ¬
"This is a Choose-From Dialog" with prompt ¬
"Pick One:" default items {item 1 of myChooseFromList} ¬
multiple selections allowed true ¬
without empty selection allowed
end tell
-Chris