The extension used for the custom objects are not collision masked like normal objects, and because of that, you can't make them solid or hurtful or anything like that. I know this because one of the first things I did in KSA was attempt to make them hurtful. The result was a single pixel was hurtful, and the rest was not. I'm not here to say it isn't possible, but it's not easily done, if it were, someone would have done it. The best thing we could hope for is the extension maker to make proper collision masks for it. I too wish this would be done, even if I'm not really playing with KS or fooling about with KSA anymore, but I don't think anyone should get their hopes up that this will be done, or even soon, or even without a lot of bugs.