Yes. First register yourself as a user at the practice where the person who needs help is registered. Once you are registered, there is an option to select 'I am asking as a Parent or Carer.' From here you can register the patient registered at the practice using their name, DOB and gender. You only have to do this the first time you put in a request for them.
Note: If you are already a patient using askmyGP at your own practice and you wish to become a proxy for a patient registered at a different practice, you will need to create a separate proxy account at their registered practice with a different email address - duplicate emails are not supported.