Or you could add one of the different non-breaking
spaces available in Unicode:
-> Normal size, although it usually does not expand with other normal spaces when the line is justified.
& #8199; -> Figure space, shouldn't be much different from .
& #8239; -> Narrow no-break space. I'd favour this one.
& #8288; and & #65279; -> These are zero-width, and have other uses.