First of all, I know this has been asked before: Button in custom Android Toast?.
This is nearly an exact duplicate, but I think that it warrants a new question based on the fact that it’s been used in apps, namely Gmail for ICS (it appears when you delete a message).
The linked question says that it’s not possible to include a button in a Toast because Toasts cannot be focused. Is this wrong, outdated, or did Gmail find a way around it?
The Gmail undo bar is’t a toast, here is how Google did it
http://code.google.com/p/romannurik-code/source/browse/misc/undobar/src/com/example/android/undobar/UndoBarController.java
I guess this answers your question.