Similar to the request in #1960224: How to create multiple worksheets, I haven't been able to figure out a way to import an ODS (or XLS, XLSX, etc.) as multiple spreadsheet fields attached to a single entity. The current behaviour, i.e. creating a sheetnode per worksheet, works nicely (using the git version of PHPExcel). Unfortunately, it appears to break links between worksheets.

Ideally, when prompted for the file to upload for import, we could add a select list to choose the entity type into which we'd like to import the spreadsheet. _sheetnode_phpexcel_batch_import_file() could then decide whether to build a bunch of sheetnodes, or add a bunch of spreadsheet fields. There should probably be some validation before proceeding with the import that the spreadsheet field will support the number of worksheets to be imported.