Can I somehow force bitcoind to do decomposition with getblock?
By looking at the source code here

https://github.com/bitcoin/bitcoin/blob/master/src/bitcoinrps.cpp
https://github.com/bitcoin/bitcoin/blob/master/src/rpcblockchain.cpp

and comparing it to the code in the pull request in the question

https://github.com/bitcoin/bitcoin/pull/886/files

it seems like it is NOT possible in the code today. Oh well.