Insurance companies stack the deck in their favor. There is no 'silver bullet' to getting covered in case of death while climbing to help you avoid outrageous rates.
There are basically two things you can do:
1. Pay for the rider which covers climbing, which as someone else pointed out will set you back. A lot. (Unless you can find a company that will cover you even with your climbing-related activities. There are a couple out there but good luck finding them).
2. Lie.
And just to be clear, NOT telling them about climbing is what they call in the biz a "material omission" that will likely void the policy UNLESS two years pass without them catching it. Thats the crux right there: any omissions or misrepresentations you make have to be caught by the insurance company within two years of the policy effective date or they are screwed, but you are golden.
Be warned though that when you apply for life insurance, you sign a medical release allowing them access to your medical records. If you have been treated for a climbing-related injury and its reflected in the medical records they will find out. If they bust you in a lie, they will cancel the policy/refuse you insurance and enter you into a NATIONAL database. Then you are effectively screwed.
I am not advocating any dishonesty whatsoever. Sometimes we forget things when filling out the application/questionnaire which is why those inaccuracies are only material for the first two years.