I don't know any way to convert automatically at import time.
What your can do:
- from the organizer: select a batch of raw files and 'export them as new file'. That creates a new set of jpegs. They are not included by default in the catalog; you may want to import them afterwards, but then there will be no 'version set' created. You could 'stack' them instead of creating version sets with the visual search option. The advantage of exporting is that there it's extremely simple and works on even huge batches.
- From the editor: use the 'process multiple files' option. About the same comments as above.
- from the ACR dialog: you can open a reasonable batch of raw files to edit them at the same time. If you set the edit to 'auto', select all files and apply the same edits to all, you can click on 'Open' which will open all files in the normal editor. You'll have to save them individually, which takes time to confirm. I suggest clicking rather on 'Done', which saves the settings to all raw files. After that, either the organizer 'export' or the editor 'process multiple file' can convert the whole batch to jpeg as explained above.