Create a parallel (hijri: islamic lunar) Calendar management to run concurrently with Google calendar and its features.
1. Currently the default entry is Gregorian date
2. AddOn: Entry can be Hijri or Gregorian date
Once entered as Hijri date, all subsequent date/event management will be Hijri as the refernce point
1st Moharram 1435 (01-01-1435H) >> 4 nov 2013 ( 04-11-2013)
1st Moharram 1435 (01-01-1435H) >> 24oct 2014 ( 24-10-2014)
As you can see the tracking is dynamic , and you will have to rely on an independent conversion engine.
Everything remains the same as in Google Calendar, with a further add on to the dates in Hijri as well (user definable), also should work well with iCal protocol
Note: This service is not meant to be free but shareware like!
Some reference to read