Create a specific order of paginated entries by entry type
If I get you right, you want to exclude the premium entries from the others? Carefull, code is not tested ;)

{% set premiumEntries = craft.entries({
    section: 'offers',
    entry-type: 'premium',
    order: 'postDate desc'
}) %}

{% set standardEntries = craft.entries({
    section: 'offers',
    entry-type: 'standard',
    order: 'postDate desc'
}) %}


Then you need to do a loop to merge the standard to the premium. 
Something like this
Merge two arrays of ElementModels?

... and finally paginate trough all of them. 
Hope that helps.