Option 1:Use Apply Parse delimted activity method on a page reference (you can check any out of box parse delimeted references to find out how to configure) to parse the string data in to clipboard. This will map the data in to whatever the properties you mentioned in the delimeted rule.
Option 2: For example, if you have a string, seperated by comma, for each of the comma seperated value if you want to create the page list and you are not sure how many values may come, then simply use, whatcomesAfterFirst option in a loop and for each each value create a pagelist.
Instead if manual java step, you could use direct function call to @(Pega-Gadgets:pxDataManipulate).pxPageListFromStringCSV which solves this requirement. Let us know if you need more information on this.