If you want to try boiling with steam try injecting steam into your immersion chiller and drain the condensate into a bucket or on the ground. This is a copy of the method used in most of the commercial multi barrel boil kettles. The large scale systems use steam @100 PSI /350 degrees in a stainless pipe coil and use a steam trap to maintain pressure inside coil and only release condensate. You should be able to reach a boil with 5-10 psi steam but will find that generating enough steam will be a major problem, it would be much easier to direct fire the boil kettle with a burner than trying to make enough steam.
I would advise against direct steam injection as the wort volume would increase,(steam injected would equal water evaporated plus heat losses), and the ability to inject steam at low flow rates into liquid quietly is not easy.
Make a flash boiler for water heating and steam for steam injection into pumped wort and you could get by with one burner under boil and one under boiler like my old system and the new phase 2 automated system.
Here is a commercial example of steam coil heating on page 5 of this link
http://www.langhambrewery.co.uk/tour.php