Fill a condom with water until it takes form like a dildo shape, now use some sticky tape to make a narrow bit in the middle. This should look like a plug. let it freeze overnight so you have a ice buttplug.
Insert it when its ice and make sure it doesnt fall out, the only thing that is allowed to fall off is the bottom end after it melted.
Do some jumping jacks and don't touch your penis the whole time until it's all water again.
Post or send me a pic when it's inserted.