Ok, this was easier than I initially thought.

Here is a patch. I've tested it with a number of configurations: a few
grouped tags, many grouped tags, grouped tags that fill the last line
entirely, grouped and ungrouped tags. Notice that even ungrouped tags
are indented by two spaces. This is done because some tags may be
grouped while other not. In case no tag is grouped this is adding an
extra initial space but I think removing it is not worth the check "is
everything ungrouped?".

Best regards
--
Carlos