Email Rob and ask him, I have a Mouse too and have emailed queries to him, he is most helpful. Here’s what it says in the FAQ section of Rob’s website on this very subject...
Can I add a magnetic pickup to my bass? this is possible in theory, but not practical or cost effective. The work for this needs to be done at an earlier stage in the construction of the instrument. In addition, special electronics are needed that can blend a magnetic pickup with a piezo. If a highly skilled repairman wants to do this work it can be done, but I do not offer this work as a modification.