I'm afraid you can't. Even if you buy Motioney PRO without the Standard Version, you will not be able to login.
Here is why:
1. Motioney Standard is the main product which is either an Yearly Subscription or Monthly Subscription.
2. Motioney PRO is an Upgrade or Up-sell which adds the PRO features in your Motioney Software.
3. Since Motioney PRO is not independent, you will need to subscribe for the main product Motioney yearly or monthly subscription first. Else you can't use Motioney with only Motioney PRO in your account.