the renamed filename to be tucked away in the IPTC data during initial ingest without having to do a second IPTC application?
If you use a predictable renaming string like I do using {year2}{month0}{day0}{frame4}
then you can use this string in any of the IPTC fields (I use it in 4 of them during Ingest just to be sure) so your wish is already done.
Just make sure you use in the IPTC the exactly same rename string you use in the ingest dialog for setting the filename.
As I see it the only case it won't work when you use a {seqn} variable as it increases each time you use it. But all other variables are constant for each photo so you can use them any time during the ingest even in the IPTC.