David N8DAH suggests you can use your µBITx stock switch and microphone element with this nifty mini-microphone case from Kit Projects. They cost US$10 plus shipping. These are 3d printed with all hardware included (Mic’s use the stock element and tac button that came with your bitx40 or ubitx).
Kit Projects has red and black microphones right now and grey is coming soon!
The also have 3D printed mini paddles available to purchase, that may be of interest to µBITx constructors.