Are silicone rubber bands safe for LEGO?
Silicone does not appear to be safe with ABS plastic
This sounded like a good idea to me since silicone works well in other extreme circumstances like baking, but the quick research I've done says this is not so smart.  I found two general references for ABS compatibility:

Plastics International Plastic Compatibility Chart
Kelco's ABS compatiblity chart

Both rate the compatibility a D, which means:

Material will decompose or dissolve in a short.

or

Severe Effect.  The material should not be used under any circumstances.

The only caveat here is that Plastics International is talking about &quot;Silicone Fluids&quot; and you're asking about a solid.  I wouldn't risk my LEGO's on that unless we hear from somebody that tried it and it worked out for them.