I'm afraid we are not able to provide much support for this solution. It was offered only as an example of how to resolve the problem as described with the limited flexibility mentioned in the postings. We had no need to build in greater flexibility for ourselves.
We have continued to use it for over a year now, including through the OS upgrade to Mountain Lion but cannot offer customized implementations. (Mountain Lion stores event records somewhat differently than Lion did; each event results in a separate file now. However, CalUpload posesses the flexibility to cope with this.)
It may be possible for someone proficient in Unix to modify the script to filter the calendar entries to accomplish what you have suggested. Alternatively you could try using it as offered and set your iCal preferences (Advanced) to then delete all events 30 days after they have passed.
Apple don't mark posts as solved - only the person who started the thread can do that, and that is what has happened here. The post he marked as a solution was made before a number of other suggestions were made, though I don't know how effective they are. Part of the problem is that a CalDav server may be required, and these are difficult to find (MobileMe was one such but at we know that's long since gone). It's possible to run your own, but only if you have suitable equipment and the knowledge to do this. (My own post on page 1 was made before MobileMe closed and is of course no longer applicable.)
Here's a simple solution (relatively speaking):
Log into iCloud and get the public share address for your calendar. Something like this... webcal://p03-calendarws.icloud.com/ca/subscribe/1/246COWhNqrt3AaAhx237JSnsjsnSJ nsjdfkjsbdfmXad8Y_pUx-WcSdrUxhHzdfbzcvbxfvbzdfbzcvbczvbgrVVYfcEaUODr048_uVBPMumF BNoDAqSE0
Plug that URL into THIS site: https://icaltogcal.com because Apple won't let Google read the iCloud feed directly, you need a proxy.
Take the resulting output which will look something like this: webcal://icaltogcal.com/share.php?c=27da9e203cd8a0a67bSDFDfJFhHFHFdhshdf53c01ff ad8fa09.04380390
Log into Google calendar and on the left side under "Other Calendars" select "Add by URL" and paste in that second webcal address. Select "Make public" and click "Add Calendar"
There you go. You are now subscribed to a read-only copy of your iCloud on Google. You can now share or embed this in a webpage like any other Google Calendar. The only caveat is when you make changes to your calendar events in iCloud it can sometimes take a few hours for the Google Calendar to refresh the feed from iCloud… but there is a solution for this as well which I have NOT YET TRIED. https://scheduleshare.net claims to be able to force Google to refresh the feed every single time it's called… for a fee.
Apple should allow read-only embedding of iCloud calendars. The fact that we have to go through all this is just stupid.