You'd have to tweak the stuff in g_text.c and probably also g_rtext.c to lie about the rectangle size, and to enlarge the bbox for what gets counted as an xlet, then recompile.

Meanwhile, there's a single tk canvas subcommand called "-closeenough" that does exactly what you want.  But Pd doesn't use that-- it only fowards mouse motion over the socket to Pd.  Then Pd core queries the bounding box of every object on the canvas, to see whether it falls within the mouse coordinates.  It does this for _every_ single "motion" message received from the gui.  (Run pd with the -d 3 flag to see how often these messages get sent.)

-Jonathan