Pagination

[mastef]

I've been playing around with the activity_get_activities pagination, and I don't seem to understand how I can use the pagination to match either one of these scenarios :

Scenario one : Show only page 2, 10 entries per page

Scenario two : Show 10 entries after activity id 242

Are any of these possible? As it is right now it seems to display simply X amount of pages, which would make a bigger and bigger response the further down I load the activity stream.