Contact support and they should be able to do it. They know how, but don't advertise the process. 

It is similar to this for convert to ProSeries https://accountants.intuit.com/support/en-us/help-article/other-articles/converting-tax-data-proconn...

Second what @George4Tacks says.

Done this before for reasons other than conversion.  So did others.

It's a manual process Intuit Support needs to go through to export the data.  So, it may take a couple days to receive a download link for your files.

Since ProConnect is run on the Lacerte engine, the files are actually in Lacerte format, which means you can import the files directly into Lacerte without having to go through conversion.