Offical rules wise, no. If you want to armor objects (to make them harder to damage) use the Vehicle armor rules. Making things stronger (i.e. more SI) requires either making them larger (use the same table, just make the object any size you want for the proper SI). or make it out of stronger material. Try this rule:
For the cost of a masterwork item (x2 cost), you can double the weight of an object for the purposes of determining it's SI rating. This reflects constructing the object from stronger materials, reenforcing the internal structure to resist damage, and so on. You can apply this twice (x4 cost for x4 weight equivilent), but not any more.
