Hi Rocco
I noticed that Pivot-node accepts wildcards so I renamed all numerical fields to num_1, num_2, num_3... and specified PivotFields as 'num_*' in the Pivot-node. This solves the dynamic input issue.
By using X-Ref and Transform, the pivoted field with column names is updated back to original.
Here's a screenshot of the data flow:

BTW, I got the Data Flow Parameters working as well in the Web Data Connector. I just had to include 'wdc' in the Data Flow propery name :)
I'll contact you in case I have further questions. Thanks for your help.