Generally, Excel caches the values of cells that are computed, and those cached values can be deliberately targeted by the Apache POI libraries. However, saving the cached value with the spreadsheet is not required, so you may need to execute the formula.
Unfortunately, Apache POI is a memory hog, and any solution to this will result in a memory spike. Consider using a single dedicated thread to do such imports, so you can't get multiple users/tabs running at once.
You can go directly from the imported sheet (in memory) to a "Prep" query, so that one-time spike is it.
If you are feeling brave, look at this topic: