You could compose a message using multiple words in the text. It does mean your vocabulary is limited and jargon terms may not be available, but with some cleve

You could compose a message using multiple words in the text. It does mean your vocabulary is limited and jargon terms may not be available, but with some cleverness you can probably get your message across. If the exact spelling of a message is necessary, you could also design your cipher to use the first letter of the word instead.