There is a block everything for a specified member in Privacy Settings. See "Block this user". It is at the end of the page. Once all the seeks are taken by others you can unblock if you wish.
May already be there but you can make a request here.
Controlling Seeks
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Is it possible to prevent you from getting games from open seeks against the same person? I don't want to stop seeking but I keep getting games against the same person, all but 2 of which I have aborted.
There is a setting which sets Max games but not 1 which sets games per opponent