I have a Trezor One with firmware 1.4.2 and I have lost the recovery seed. I'd like to send a transaction from the device to another address that I control. However, because of its outdated firmware, only older versions of wallet software can interface with the device. I've found that Electrum 3.0.6 is the latest version of that wallet that can work with this firmware.

The firmware update process on certain versions will wipe the device, and if the device gets disconnected during the process it will be wiped. So I'd like to avoid the firmware updates until I'm sure that the coins are in a wallet I can control.

Would it be possible to create an unsigned transaction on a newer wallet without the private key, then somehow signing it manually with the device before sending it to the network using the newer wallet?