edit your link_add.php file located within the admin directory
scroll down to the "// verify input" comments , roughly line 112 and you will find
Code:
Content visible to License Owner only.
this is where you can disable the $url as compulsory and should work with email to.
to disable $url delete the
Code:
Content visible to License Owner only.
line (or comment out)
to disable $email delete the
Code:
Content visible to License Owner only.
line (or comment out)
save.
Then you have to edit your add_form.html and remove
Code:
Content visible to License Owner only.
line, and
Code:
Content visible to License Owner only.
save,