Cleaning oil pan sludge without dropping it- before changing to detergent based oil

[dfclimber]

I am going to be switching from non detergent oil to detergent oil
My car is a driver not a show car with an original motor
My oil pan has not been dropped and de-sludged.
I do not really have the time right now to get the gaskets and drop the pan.
I am going to be changing the oil soon at the end of the season.

Does any one have a recommendation in changing the oil when going to detergent oils.
----ie drain the old oil, close- add "magic detergent" or kerosine let sit to desludge-drain and then fill with new oil- done?

Thanks
D