Okay, so to summarize what I got out of that, in my PE environment in order to get SFC logs, I'd need to:
Assuming the offline Windows drive is drive F:
Set the variable for the log file, so SFC doesn't attempt to store to log to the read-only media:
Run SFC with offline parameters:
sfc /scannow /offbootdir=F: /offwindir=F:\Windows
Once that command has finished, it's output should be logged to F:\TEMP\CBS.log, or wherever else you specified.
So to pull the errors out of the file, run:
findstr /c:"[SR]" F:\TEMP\CBS.log
This will output all error lines to the command prompt, if you want that output to go to a file instead, run:
findstr /c:"[SR]" F:\TEMP\CBS.log > F:\TEMP\sfcdetails.txt
Now your details regarding the failed repairs should be contained in F:\TEMP\sfcdetails.txt
Hopefully anyone Googling how to use SFC from WinPE in the future will find this helpful!
Also, thanks Brink, I appreciate the help, very fast, very effective