In CompuStat North America you can add CIK number to your output. This identifier is recognized by Thomson One Banker, so that could mean that you can change the CIK into ISIN, SEDOL, DSMnemonic, etc, and use them in Datastream.
I’ve tried it with a list of tickers, uploaded them in CompuStat North America and requested the CIK. Then I used the PFDL-function in Thomson to retrieve the ISIN-codes. It worked fine, but unfortunately the first CIK-number wasn’t recognized by Thomson, and caused an error-message. But: 172 cik-numbers (undoubled) gave 164 ISIN-codes and 166 SEDOLs. Please click the picture to make it larger.