I've simply learned the rounded sines for angles of whole ten degrees off by heart long ago and this works perfectly well for me. If this is to much mental arithmetic for you, you might try the following rule of thumb instead:
CWC ≈ [(wind angle / 100) + 0.2] x wind speed
Example:
RWY 27, wind 31012KT
1. step: wind angle is 310 - 270 = 40 degrees
2. step: 40 degrees/100 = 0.4
3. step: 0.4 + 0.2 = 0.6
4. step: CWC ≈ 0.6 x 12 kt ≈ 7 kt