I did some cursory browsing of the WebView and WebViewInputDispatcher classes, but didn't come up with anything. Maybe you could take a look there.
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.2.2_r1/android/webkit/WebView.java
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.2.2_r1/android/webkit/WebViewInputDispatcher.java
My thought was that perhaps you could pinpoint where the blocking occurs and either extend those classes or create your own copy and modify them.