By and large you still can do it via GUI. Launch client ==> check "Standard wallet" ==> Click Next ==> check "I have already a seed" == > Click Next == > Click Options == > check "Bip39 seed" = > Click OK == > Enter your BIP 39 SEED ==>Click Next ==> check "legacy (p2pkh)" (you may also change the last index in derivation path if u know what you are doing) ==> Click Next
He doesn't have to do that. Electrum allows you to create a legacy wallet without having to import any BIP39 seeds.
Why? Bag and baggage, the private keys only matters. Is there any essential difference in private keys generated from BIP39 SEED and native Electrum SEED? The procedure to create the legacy wallet via Electrum GUI is much easier than via its console and eliminates human errors.