There are no loopholes in the regulation!  

is not rest.  Therefore, it can't be counted as rest.

If you are obligated to the company to work or be called to work at any time (beeper duty, pager duty, stanby duty, whatever), you are not on a rest period.   You don't have to call it "duty".   You have to call it "rest" for it to be useful.   The regs clearly say that you must be able to look back 24 hrs from your planned landing time and be able to show 10 hrs of continuous REST in that 24 hour period.

So, if your certificate holder sends you home, whether for pay or not, and tells you you need to be on-call to come back in, you are not on rest and can't use that time period towards your need for 10 in 24.

For you to be on a REST period, the certificate holder must release you with no obligations to be at their beck and call.   If they send you home and tell you that you are obligated to begin answering your phone again after 10 hours (or whatever hours), you rest ended at that time.

You can be on duty, on call, on beeper duty, etc, for as long as forever.   But, you can't FLY a Part 135 flight if you can't look back and show 10 hours free of all constraint in the last 24.

So, what that means is, you can be on call as a pilot for 24/7 for a whole week.  And, for them to use you, they will have to call you and put you on a rest period of at least 10 hours to have you THEN come off of a rest period.   That will reset your clock to limit you to another look back requirement.

You are not limited to a 14 hour duty day.   You are limited from flying under Part 135 rules if you can't show a 10 hr rest period in the 24 hrs look back from your reasonably planned landing time (not your planned duty off time).