Questions on hybridization of atomic orbitals..

For hybridization to occur, must electron always be promoted? Is it possible for hybridization to occur without the promotion of an electron?

Secondly, if electrons DO need to be promoted, must there be at least one completely empty orbital in the shell it is being promoted to?

For example, say an electron is promoted from 2s to one of the 2p orbitals. What if every 2p orbital already had 1 electron? (a configuration such as [math]{2s}^{2},{2p}^{3}[/math]). Would an electron still be promoted to one of the p orbitals to make a configuration like

[math]{2s}^{1},{2p}^{4}[/math].. (my problem lies in the fact that after promotion (if it does occur) that there will be two electrons in a one of the p orbitals... Can that happen in when electrons are promoted?