I guess it really depends on how much power they can transmit.
If you get a lot of power, the simplest concept Would be an electric heater to increase the temperature of the propellant above what it could get through combustion. The higher the temperature the greater the expansion and the more thrust per pound of propellant is obtained.
That's essentially how a jet engine works but replacing the combustion chambers with electric heaters - and it sounds really expensive in terms of power consumption. An alternative is a kind of plasma propulsion engine called a VASIMR [0] engine.
I don't want to do the napkin math but my gut is the most practical electrical mechanism to get enough delta-V to LEO is a railgun but doing the acceleration up front would have probably have undesirable effects on the payload.
If you get a lot of power, the simplest concept Would be an electric heater to increase the temperature of the propellant above what it could get through combustion. The higher the temperature the greater the expansion and the more thrust per pound of propellant is obtained.