How to display an orderly list from a number of selected text variables?

There's a first time for everything, here's my first time posting a question on this forum :-).

Project information:
I'm working on a Storyline project that has over 30 text variables. Each text variable has eigher nothing assigned or a text string. By pressing some buttons a learner will ultimately select a smaller number of these variables (let's say in the range of 0-10). When selecting a variable it will have a text string assigned. When deselecting a variable nothing (e.g. a space) will be assigned. A variable may be toggled by pressing a button over and over again (probably pointless, but possible). So far so good.

During the selection proces a text box is visible to the learner. When hitting a button the corresponding text string should appear in text box, hitting the button again should remove the text string. Ultimately all text variables that have a text string assigned should be shown in the text box in an orderly manner. Either in a one column format, or separated using a separator (like a comma).

I've been able to more or less create the above but have trouble with getting an orderly list. In my current solution I have a text box with the all possible  variable names in the display notation (%variable_something%). The problem is when a learner has for example selected the first and last variable the corresponding text strings are shown but they are separated with a huge number of new lines (caused by the variables with no valid assignment).

The question:
Is there an elegant way to implement this so a learner gets a nicely ordered list of, e.g. 5 items, with no newlines in between? (and the list should be updated in real time).

I hope there's someone out there who can give me some directions on how to go about this. Thanks in advance!