Unfortunately there is no possibility to add a custom shortcut through the application user interface. However it is possible to modify preference files as you want. For that you need the modify .xml files in "plugins" folder located in the installation directory.
For an example, I've defined a shortcut for Sketch Point feature by adding the following line in plugin-Sketch.xml file:
<!-- SketchPoint -->
<feature id="SketchPoint" title="Point" tooltip="Create point" icon="icons/Sketch/point.png"
keysequence="Ctrl+P"
helpfile="pointFeature.html">