Speaking for myself I'll probably use a spreadsheet. But then again, not everyone is as proficient as me using Excel.
Like tarek suggested JSudoku is best for this task, as it has the option to automatically export all puzzle states into the single line format.
Also Simple Sudoku can import a PM and then export into a large block of various text formats, one of them is equivalent to a puzzle grid (well you can't distinguish between the solved cells and the original clues). Using the "replace all" feature in Notepad/Word etc it's very easy to transform the grid into the single line format.