Thanks for your time.
Its the other ways around sir.
First you need to have at least 1 EOS token on a wallet for the registration to actually go through. That means you will have to move the tokens to your private wallet in the imtoken app.
What that actually mean is you get your own Main EOS private and public keys which is mapped to your ethereum wallet and as soon as the EOS main-net is launched it will take a snapshot of that MEW linked to your EOS Private Keys and give you the exact amount of EOS coins, which can be imported through your private key.
I do hope this have answered your question!
RE: HOW TO REGISTER YOUR MEW HOLDING EOS WITH IMTOKEN WALET APP.