Custom options for each selected columns

I'm creating custom table visual and I want to create options which can be set to each selected column - in the same way as it is in build in table visual.

I saw the answer from this topic custom visual enumeration issues, but the solution proposed there don't add combo with selected columns, but create a separate option for each selected column.Using this approach will take a lot of space in Format pane 

I want to add many options for a single column, so using this approach will take a lot of space in Format pane.

So anyone knows how to create combobox with selected columns names, create options for each and handle selected values?