Yes you can but you'll need to be a subscriber with MiScore ($16.49 per year)
When you add a club that you are not a member of and select to 'comp score' - the app will check if you are a subscribe, if so then
it will automatically check the clubs list of registered visitors in the comp and match by your surname. As long as you are registered and have paid your comp fee,
you should be able to select your name from the match selection. Once you've done this then you will be asked to select the player you will be marking for.
If there is no match, check that your app profile has your correct surname applied, if not update as required and try again.