This can be achieved using the Editor. For each World Size, you can set the total number of players to anything up to 31 (the 32nd is always the Barbarians).
Wouldn't recommend putting 31 Civs on a Tiny (60*60) map, though, because the map-generator will tend to run out of 'valid' starting positions fairly quickly -- and once that happens, all the remaining initial Settlers usually end up getting placed directly adjacent to the first starting-location, i.e. yours! (The human-controlled Civ always gets the "Player 1" slot, by default).
You can, however, also adjust the World-Sizes. So you could make a Tiny map measure 90*90 tiles (+50% in each direction, i.e. 2.25x more tiles in total), and then have, say, 9-10 Civs instead of 4.