If you are taking off to the north ( 000) and the wind is 030/10 then I assume you know that 30 degrees is 0.5 and therefore you have 5kts crosswind.
If the wind was the same but you were departing off 09 I bet you could work out the crosswind too, 60 degrees off therefore 80% = 8kts.
The crosswind in the second example is the headwind in the first example. So all you need to do is subtract the 30 from 90 and then apply the sin rule of thumb you have and you have your headwind.
All you need to learn is the basic sin rules.
30=0.5
40=0.6
50=0.7
60=0.8
Another example to show you;
Departing to the north.
Wind 050/10
Crosswind = 10x0.7 = 7kts
Headwind = (90-50) = 40 now apply the sin rule of thumb to get 0.6
= 0.6x 10 = 6kts.
Simple
the only thing you need to know is the four sin rules and the fact that you have to subtract the "degrees off" from 90 if it is a headwind you are after.