I think this should be doable with 'asfunction', look it up
in the help. You can make a link that triggers a function, and in
that function do the loading. Your XML node might look like this
then (not sure about the asfunction syntax):
<node label="How to start an new activity"
BTW: the root node should have an unique name by XML
standards, so it's better to change it to <nodes> or
something like that.