While probably not best practice, you can use the map function in conjunction with loadjob (as you mentioned) for a thing like this. Assuming your base result set is not massive, you can store it in a lookup table (haven't tested with KV store but don't see why not) and re-attach it to the results using lookup. If anyone knows how to make map simply append the results like a join instead of replacing the results, please chime in.
YourSearchHere | outputlookup tempForMap.csv
| map search="| loadjob $sid$ | eval sid=$sid$" maxsearches=10
| lookup tempForMap.csv sid OUTPUTNEW
Note that the above assumes your SIDs are in a column called sid. If you can share additional information about the larger objective here, maybe there's a better way.
Please let us know how it's panning out or if you found a better solution.
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