You could do it with clothes that are not your "good" ones.
If you just need more bulk in the washer to make it work right, you don't even really need to use DIRTY clothes. You could pull out your oldest, most worn/stained/faded things, and throw them in for the purpose. If certain kinds of things work better than others-- like jeans vs. t-shirts-- then of course use ones of the right type.
I worded that weird, what I really meant was my clothes in general not just the particularly good ones or anything. But that is a very good point. Last time, I used old jeans that I hardly wear anyway, so I suppose there's no harm in running them through again even though they're clean now.