Probably it could be done.
But you're breaking a rule/principle for good OOP design, don't remember what exactly it was

So, this turn out as a feature of C::B's CC, not a bug :lol:

(I'm joking of course)
Have you tried to lower the number of result you can have in the auto-completion list box?
The default is pretty high and if your query is too generic filling the list will be the most expensive operation.