<p>Earlier versions of the Notes client would automatically turn a <em>sent</em> URL into a clickable link for the recipient (regardless of mail client) but with 6.5 (and presumably later) this no longer happens; that is, the URL is sent as plain text. The Notes UI allows it to be done via the Create->Hotspot->Link Hotspot menu but this gets tedious.</p>

<p>I'm looking for a way to create a Link Hotspot in LotusScript. My research to date leads me to believe that this isn't possible but there may be a hack of some kind.</p>

The automatic conversion of urls into clickable links is a user preference.
In 6.5 it is set via File/Preferences/User Preferences/Basics.  In 8 it is set via File/Prefences/Basic Notes Client Config.
I don't think you can create a url link hotspot explicitly using lotusscript.  You can create a doc link, but there is no obvious way to turn it into a url link.
You could try an approach where the form is set to render passthrough html on the client and then construct the relevant html for a link.
Update in response to comment.
The scenario is that we want to to control what a user receiving mail sees.  We have a few cases we should think about.
The recipient is using Notes and received the mail directly via notes to notes routing.
The recipient is out on the internet using any client and allows email in a rich format.
The recipient is out on the internet using any client and only allows email in plain text.
In the first case the user will see links if they turn on the option for that.  You could also create pass-through html in the rich text and that will render on the Notes client assuming the form option is set in the design.  If it's straight email and you don't really need any other rich Notes features you could also construct a  MIME message.
In the next two cases you just want to send properly formatted MIME messages.  In the first of those cases the user will accept rich formatting and therefore you can construct the message as simple html and include links that way.  In the second case the user will not, and you have to make do with plain text.  Luckily most mail clients will automatically turn urls received in plain text messages into links for you.  This may be an option as in the Notes client.
It is best practice when sending rich mail content to also include a MIME section for plain text.  That way you don't need to care what version the user prefers.