One idea I can think of is to maintain 2 arrays (lets call one of them Main and other Extra). Our Main array is single dimensional with the data to be shown in the list view. The Extra array is a 2D array with the first row containing data for the 50th item in the list view, the second row containing data for the 100th item in the list view, so on and so forth.
We can then inject dummy objects at 50th, 100th, 150th ... positions in Main array. In your adapter's getView() you can then check if the position is a multiple of 50 and get the corresponding data from Extra array and supply to the slide view.