Basic starting theory is to get enough air moving to pressurize the burner area and atomized the fuel within the combustor.
and then the three S Spin Spark and Spray.
The air flow you want is that going through the turbines (not out the fan) as the core flow helps to overcome the drag in the compressors.
I suppose that if you put enough starting torque on any rotor you could generate enough positive torque in the turbine to drive the compressor in front of the burner high enough to pressurize the burner and lite it off