You will need to create some empty formulas in the report  header sections and then you should be able to use code pass in the field values from the dataset tables. These formulas become part of a collection and you can reference the collection by name (a string) or the index number (an integer). For simplicities sake I always use the name.

Without looking, I believe this is done using the datadefinitions properties, though the .Net help file will give you the correct syntax for the object model.

Sorry my mind was seeing a different question than the one you asked. I was trying to make it harder than it needed to be. You should be able to  create the dataset and put the datafields wherever you want them. I do have some recollection that  CR likes the datasets to be strongly typed. The subreport solution is one way but depending on what you want to do may be not be needed.