Question

When a pokemon is evolving, can you stop it from evolving some how but still have it gain levels afterwards?

Answer 1

To save time, yes.
1) Press the B button
2) Give it the everstone

I think these are all the was to level up pokemon that are evolving.

Answer 2

This has already been asked

http://pokemondb.net/pokebase/5175/can-you-stop-evolving-your-pokemon-but-still-raise-his-level