If you were designing for the appliances as a new install,you would be wise to follow the guides that recommend a dedicated circuit for the cooker,with a separate radial and perhaps off the local ring to the dishwasher
However, you are working with what is existing and you may consider the need to deviate from those recommendations that are in the guides,if you can still ensure safety
The use of a dedicated circuit for a cooker is a recomendation,follow that recomendation and you won't ever go far wrong,however,a recomendation does not mean"You must"
The first thought would be that the 6mm radial will most probably have already been de rated by the use of a 32 amp mcb at the supply end,depending on installation method,overload may not then be a problem (other than a nuisance factor if the mcb happened to trip occasionally if it was overloaded for a period of time)
Your opening suggestion,although not a standard arrangement appears to be a suitablee compromise,however,the cooker control could be changed to a straight DP isolator,doing that will reduce the possible unknown extra load from the existing cooker control integral socket
In short,if the posted information given is correct,it would not cause me nightmares if it was necessary to adapt such an arrangement to my own kitchen