Try this:
In QS preferences enable advanced features.
In the Quicksilver section of Catalog enable proxy objects.
In the Extras section of preferences enable pull selection from front
application.
Restart Quicksilver.
Go to the triggers pane and click the plus sign to add a hotkey
trigger.
A command window will pop up. Select the Current Selection proxy
object in the first pane. Select your applescript in the second pane.
Press return.
Double click the newly created trigger. Press the key combination
you'd like to use.
Close the preferences window, select some text and press the key combo
you just set.
Let us know how it goes
