Yes, I asked Pentax what they'd recommend. Please check the link in their reply:
Dear Ole,
Thank you for contacting Pentax.
Not all K-5 cameras are affected by the sensor "stain" problem. The K-5 review page on the Enticing the Light Web site has excellent information on how to distinguish between dust on the sensor and an actual sensor “stain”. It also has a very good assessment of the actual effect of the stain on images. We encourage you to visit the link below for this information.
Review - Pentax K-5 | Enticing the Light
If you have confirmed that your camera has this sensor problem please reply to this email with your complete US mailing address AND your email address and PENTAX will send you a pre-paid UPS shipping label to use to send your K-5 camera to our service center for examination and warranty service. The earliest that the service center will be in a position to address this problem is after the holidays so you may wish to delay sending in your camera until next month. However, you may be assured that if it is confirmed that your K-5 has the sensor problem it will be handled as expeditiously as possible under your PENTAX warranty.
If you are in need of further assistance, please respond to this email or call our technical support center at 800-877-0155.
Sincerely,
Randall S.
Pentax Imaging Technical Support