Have seen in a number of articles the use of silly putty for masking. Here is something similar, looks very versatile. Together with a bunch of other strange stuff.
Here's an example of it being used: http://www.xtrememodelling.com/foros/viewtopic.php?t=582
Here's an example of it being used: http://www.xtrememodelling.com/foros/viewtopic.php?t=582