Hi Mark,
I believe that it is possbile. You may customize JS solution from this post:
https://forums.caspio.com/index.php?/topic/3200-js-concatenatecombine-two-fields-into-one-field/
You need to change element_id to reference Virtual field(correct syntax: cbParamVirtualX ).
You may also need to change an event trigger i.o. onsubmit.
Hope this helps.