Not sure how you'll be able to do it. Even up high you're still just getting tropospheric scatter from Seattle so height won't help you.
Maybe a horizontal/vertical stack of 4 of the highest gain antennas you can find. I like my 91XG, maybe that would be a good choice.
Worth trying perhaps but realize you may end up with an expensive experiment that doesn't provide useful reception.
You could start with a single 91XG and see if you can find a location where you can fit 4 of them and at least marginal reception. If you get any reception at all under ideal conditions then the 5 dB of additional gain that you could hope for from an array might be enough to give you something usable.
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