That's not really parsing it if you have to parse it first.
Jethro_ Said:

You merely need to specify one +b or -b to have all the strings prefixed with a channel mode.
Half of the goal of my parsemode alias is to pair the mode up with the nick or address it is being applied to.

I'm sure there are a lot of other ways to parse the rawmodes but your alias doesn't get it done.
The idea is to parse the rawmodes , just as they are returned from the event..
From your example:

//echo -a $parsemode(+b this that theother)

This should have been::

//echo -a $parsemode(+bbb this that theother)

With your code this would return::

+bbbthis +bbbthat +bbbtheother

I don't think that output would serve any purpose here.

Thanks for the comment. It just reminds me of what a headache it is to parse rawmodes properly.