you don't. In theory you can sign a transaction with any node you can access via RCP. But you need to know what you're doing. Best solution is having keys on a pen-drive with PGP and an offline device like an old laptop. You put Electrum on that laptop, create a new wallet with seed, backup that seed and then forget about it cause you wont need it, ever.

Then, when you want to move coins on-chain you'd plugin your usb stick to the offline device. Import the key you need to that wallet, sign your transaction, download the tx to a different usb drive and then you can delete the private key again from that wallet.

Then you go to your online machine, open electrum and transmit the signed offline transaction to the blockchain. done.