Search and Cache Mode - how to always search on the server

So far we didn't use the Cache Mode and connected directly to the exchange server. 
As this causes quite some troubles, we tried Cache Mode. This solved all troubles, but one new came up: 

We do only cache for 1 months (storage reason on local SSD's). 

Now if I search, it first searchs locally, then I have to click search on server. 

I tried to disabled indexing locally, then the search doesn't work at all anymore (greyed out). 

What I try to accomplish is: 

- no local index, it should always search on the exchange server, without the need to click (Search for more messages on the server). 

How can I accomplish that. 

Thanks
Patrick