Ahhhh that would require something slightly different I believe... as it seems you're trying to get the "BIP39 version" of an Electrum seed.

Generally speaking... an Electrum generated seed will not be a valid BIP39 seed (there are some relatively rare exceptions). So, if you click the "BIP39 seed" and type in an Electrum seed, it will likely show "checksum: failed". Electrum will allow you to go ahead and use it anyway if you really want...

But, to the best of my knowledge, there is no way to replicate this behaviour with the Ian Coleman tool (or the tool I posted). However, it should theoretically be possible by simply modifying the Ian Coleman tool to ignore the checksum calculation.

I'll have a look into it over the weekend and see what I can come up with (if someone else doesn't beat me to it)