in a similar case we use another way: instead of offering a pre-defined dropdown, we added a list of items to a new panel at the top of the workspace project. that means, the user gets a list of the desired items (even new ones) and can "drag&drop" the desired item to the "panel" below.
in detail: we added a new "panel" at the top of the final project. in this panel, we created a segment to only contain the desired values (eg. in your examples a list of trackingcodes matching a pattern). we even added one single table with just the dimension (trackingcodes & pageviews). in this table the single items (in you case the items for the drop down) are displayed.
the user can now just select the desired item and "drag&drop" to his project panel below. this is sometimes a lot easier than selecting from a long list of items since the table allows filtering/sorting and much more...
and if the user want to send the data as PDF, he can. just collapse the top panel (with the "helper table") and he gets almost the same as with a dropdown.
the advantage is the dynamic table to select the desired item. but it needs some more explanation to the end user, but no big issue to set up...
The panel drop zone now has drop-down filtering capabilities. Dropdown filters enable analysts & end users to interact with the data through controlled filters. You can create a dropdown filter from any component type, and then switch between items in the dropdown to filter the panel contents
I use the segment box at the top of the free form table for drop downs.
I believe you can hold the shift key and select each variable from the dimension list.Then if you drag all of the selected variables from the dimension box over to the segment box, an option will appear - + Add (Press "Shift" to create drop down).
They should be able to click that drop down and change it to whatever you have selected.