Worked it out !
Create banner as normal with clickable button but make the URL something like WWW.REPLACE.COM so it’s easy to spot in the code !
Edit the HTML head and add in:
<script type="text/javascript">
var clickTag = "http://www.whatevertourlinkis.com"; </script>
Then open the ‘…hype_generated_script.js’ file in your preferred editor - I used Dreamweaver.
Over type the URL (WWW.REPLACE.COM) with:
href="javascript:window.open(window.clickTag)"
It appeared twice in my file.
That seems to work - just waiting to hear from the host to see if it meets their specs…
Phew
Bob