GtkTextView and starting selection from derived widget

[Krzysztof Foltman <kfoltman onet pl>]

Is there any way to start the mouse selection mode in GtkTextView from a 
derived widget ? What I need is something like calling 
gtk_text_view_start_selection_drag, but:

 1) available outside gtktextview.c, and
 2) with selectable selection mode (character, block or line).

If it doesn't exist (my brief look at gtktextview.c says it doesn't, and 
that's why I'm posting it to this list), can it be added ? It would be 
useful in some situations, for example to make click on editor's margin 
start a line selection (like in scintilla/anjuta).

Krzysztof