This sounds like a case for a 1-of-2 multisignature. Create this multisignature from both user's addresses using addmultisigaddress (on both nodes) and send the assets to there. Those assets can then be spent by either user, sending back to their regular address.
Of course this only works if you trust both users to be honest. If not, you can use a 2-of-3 multisignature, where some additional third party is used for dispute resolution. If the two original users have a disagreement about where the assets should go, then this third party can resolve this situation.