i don't know about allowable! but language use is, or can be, a creative process. if the primary aim is to communicate, then rules should be evaluated on a pragmatic rather than a legalistic basis.
you have a reasonable but non-standard communicative task, so rules are less likely to give the guidance you need. common-sense suggests that (if we are dealing with written language) some para-linguistic markers would be required, taking the place of emphasis, change of tone or accent, facial expression, gesture &c in spoken language. the means available may depend on context. twitter lacks font markups, so the convention of using parenthetic asterisks has evolved.
your best guide would be to study what previous writers have done, although it is not easy to obtain that information with the current rather rudimentary query facilities offered by public search-engines. (you could try writing to MI5 or the NSA).
my own unconsidered preference in this case, avoiding the pitfalls of over-elaboration, would probably be hyphenation. to give a silly example:
he seems to like talking to people, but when you look more carefully at what he says it's mainly hail-fellow-well-mets and how's-your-fathers.
the plurals look odd, it must be conceded, and i would personally not wish to compound the felony by inserting the bogus plural apostrophe-'s' which seems to be gaining currency. however despite the marginal infelicity, few would mistake the meaning, unless they were unfamiliar with the expressions themselves, so the communicative criterion enunciated above would be satisfied. your meaning would be conveyed.