Yes. You create these via "create assets" -> "makeclothes". The UX isn't great yet, but if you create a full body "clothes" with the alternative mesh, you can then:
* Save an MHM file somewhere
* Rename the file so it has the extension ".proxy" instead of ".mhclo"
* Copy the .proxy and the .obj file to your user directory /data/proxymeshes/subfolder_with_the_name_of_your_proxy
You can find the path to your user directory via the button on the system and resources panel.