Right Plant Wrong Soil !

I have three large potted Rhododendrens approx 1.5 m high which are becoming too big for the patio. I would love to plant these in the garden but unfortunately I have chalky soil which I know they are not suited to. My question is .. is it possible to treat an area with eracatious (excuse spelling) soil and feed etc to put them in, or ... I believe I have read cases where people dig holes and put the pot (plant and all) in the ground? As you can imagine the latter would involve quite big holes being dug to incorporate these large pots !  Any advice welcome, Thanks