well, to turn it into a sloid blaock you can mix it with plaster of paris, but to turn it into putty you can mix the stuff with some rubber glue!
you need about 20% glue.plaster of paris to 80% thermite
if you do this, i'd advise throwing in a healthy amount of magnesium powder to make it easier to light, and light the stuff with a sparkler in plaster of paris.
try lighting a bit of the basic stuff (just iron oxde + aluminium) on some concrete at night, and watch the surrounding area be lit up brighter than daylight!!