What I have done, and it works (at least for me) is this:
I created a field called [link] in my structure. This allows me to add a link when entering and also is handy to identify the link to visitors as soon as they enter the details.
When entering the event details, I simply enter in the html code for the link (i.e. a href="... as you would see in the source code) along with the text you want the visitor to see.
That then creates the link for visitors within the event itself without having to mess with the SSI templates. If there is no link, I just leave it blank.
Hope this option helps some.
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