Is it possible to modify datetime so that the check_time_args function in the datetimemodule.c does not error when given a seconds value of greater than 59?  I was thinking that if the seconds were greater than 59, the seconds are set to 59 and any extra seconds are kept in a book keeping "attribute" (not a real attribute because its C) that is accessible from the Python side?  You would have to make the seconds argue passed by reference (thus returning a modified second).  Also would want the book keeping value to be zero in nominal conditions.
This would do nothing for any of the datetime arithmetic, but that can be handled externally.