REALLY SAFE way (if you can call playing with your WE that way

) should be some minor in asia/africa. Just get 2 provinces in one war. Then start another. Let enemy occupy those provinces. En tact war taxes (to earn some, and to get +1 WE).
1) Make sure that your WE rise slowly. So you can end war when WE is high, but not that high.
2) Do not increase WE in any other way. As other ways (attrition, naval blockade) will weaken your military or economy. Never a good thing.
Alternative would be to get some fresh colony (turned into city) blockaded by pirates. Then DoW some land locked african country. Pirates add to WE during war by naval blockade.