Make sure you refer to the text and music/TAB for each example as it's often easier to 'see' these rhythms than to hear them at first. It might help to print or write the rhythms out and then identify each 3/4, 5/4 or 6/4 rhythm repeat within the 4/4 marking them off as you go.
Good luck with these ideas. You can experiment almost without limits here. The variations are limitless!! Any rhythm in an odd time signature can work as a hemiola.
See you soon,
Let me know how you get on in the forums! Tom