5million, yes you are allowed to do that. I too have done this numerous times. I often jumpseat down to Houston to visit my folks, stay a day, and then use a ticket to fly home from there.
BTW, the "travel within 3 days" in the contract has been interpreted by crew travel audit to mean 3 CALENDAR days, not 72 hours from the end of your trip.
But, like all questions that involve deadheading legalities and monies, when in doubt, ask crew travel audit and contract enforcement. DO NOT depend on advice from these boards to make decisions that involve legalities with the company.