In that case, could you proof it by mentioning Steemit somewhere on the site? It could be a simple:

"This post has also been featured on [Steemit](link to this post )"
and write something like this here:
"This post has previously been published on [my blog](link to your blog post )"

Or write a Steemit post on this particular Wordpress site, or link to it on a different page...

I've linked to my Steemit account on a special "Links" page, but I see you don't really have that there, so maybe the other option is easier.

We have a lot of plagiarists here on Steemit and it's sometimes hard to figure out if someone is who they say they are. Some very talented artists have had a case of stolen identity here and these imposters got away with a lot of money through plagiarism. It makes Steemit look bad and makes us feel stupid for voting for them in the past.

Please understand that I'm not asking this to piss you off in any way. I'm a little scared to vote on good content from new people who haven't proven their identity yet (if their content has already been published somewhere else), and plenty of others here are too. So if you re-post from other blogs, you should proof it's actually you who owns the blog through a double link (from here to there and from there to here).