As long as you know a maximum number of columns, it's possible to do this after a fashion.
First, name the columns with a result from your query, so you can either pass it in to the query or derive it there. Second, just build out the report as if it had the maximum number of columns, and hide them if they are empty.
For example, I had to build a report that would report monthly sales numbers for up to a year, but the months weren't necessarily starting in January. I passed back the month name in one column, followed by the numbers for my report. On the .rdl, I built out 12 sets of columns, one for each possible month, and just used an expression to hide the column if it were empty. The result is the report appears to expand out to the number of columns needed.
Of course, it's not really dynamic in the sense that it can expand out as far as you need without knowing the upper bound.
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