Ways of testing LT HR with only a heart rate monitor

[HillRPete]

What are good protocols to estimate lactate threshold HR for those of us without a PM?

In the article below Friel/Monnier suggest to do 30min all-out, and take the average for the last 20min: http://velo-fit.com/new/pdf/intervals_vn_04_05_2004.pdf

Anyway, that's very high for me, my tested LT HR is around 165, but I can go in the low 180s for an hour.