There may be a more 'official' way to do this but here is how I've accomplished this. Create a new line item in the module you are importing into. Once you have the data imported, do a straight reference formula in the new line item pointing at the original (where your imported data resides) . Once you have entered the reference formula and all data has populated, simply delete the formula itself. The data will now stay static and not update as there is no longer a formula.
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