Cloned event pokes could be something that people would be interested in, but you wouldn't be able to use the GTS... I guess it's not very practical :/
As for snipes, you shouldn't worry too much about it. You're already doing everything you can! What you could do is add a 'status' in the first line of your post, saying whether you're online or offline at the moment. Then you'd only have to edit that before you go offline, so that people know when they shouldn't bother putting something in the GTS. I did that in my giveaways, and (although some people ignored it) it worked pretty well.
As for snipes, you shouldn't worry too much about it. You're already doing everything you can! What you could do is add a 'status' in the first line of your post, saying whether you're online or offline at the moment. Then you'd only have to edit that before you go offline, so that people know when they shouldn't bother putting something in the GTS. I did that in my giveaways, and (although some people ignored it) it worked pretty well.