I don't think it works, though its been years since I tried that, I think the requirement of beating the super version of Lavos' first form is needed for the developer's ending.

Really the toughest ending to get is the ending where Crono actually talks (its the Lucca/Marle debating all the guys looks ending) cause if memory serves me correct that required several conditions that almost amount to getting to the end of the Ocean Palace and then backtracking out of there from the last save point, otherwise you get Magus' ending or you get the Developer's ending if you face Lavos in the Ocean Palace. It's requirements are only slightly off from the same requirements for Magus' ending.

Basically the ending work by just challenging Lavos at different time periods, choosing to destroy the Epoch, or even beating Lavos without resurrecting Crono. As far as I know, there is two anime endings for the PS.DS versions though I think the DS version just through them together whereas the PS1 version required you to beat the game twice to get both. The first one is the wedding of Crono and Marle, as well as seeing the rest of the cast getting along, ending with Lucca discovering a baby (Kid). The second one is a time line showing the fall of Guardia and the lost of the Masemune and basically details events leading up to Crono Cross.

The DS version has a new ending that finally gives away what happened to Magus at the end but that requires beating the game's new secret boss.