Try this:
var input = document.getElementByID( ... )
// create the autocomplete for the input
(...)
input.val = 'whatever' ;
google.maps.event.trigger( input, 'focus', {} )
Problems:
- For some reason it does not always work (1 in 1000 times it does not request the service)
- Sometimes happens to get the suggestions of the previously introduced string
Good coding!