Unless I'm misunderstanding the original question, we seem to have gone off the track a little. Wetsuit just wants to find out if BTC/DOGE addresses are eligible to claim, right? Why would there be a need to sign a transaction by sending funds? Import the private keys and rescan the blockchain.
I'm just getting nervous about what will happen if a good portion of those "hundred thousand addresses" are eligible to claim.
I expect the quotes are apt.
That said, the proof is in the pudding
Regardless, a concerned user could indeed sync, block/unplug/firewall and check - without exposing the client to the outside world when it touches the private keys.