Force MySQL to use two indexes on a Join

I am trying to force MySQL to use two indexes. I am joining a table and I want to utilize the cross between the two indexes. The specific term is Using intersect and here is a link to MySQL documentation:

http://dev.mysql.com/doc/refman/5.0/en/index-merge-optimization.html

Is there any way to force this implementation? My query was using it (and it sped stuff up), but now for whatever reason it has stopped.

Here is the JOIN I want to do this on. The two indexes I want the query to use are scs.CONSUMER_ID_1 and scs_CONSUMER_ID_2

JOIN survey_customer_similarity AS scs
    ON cr.CONSUMER_ID=scs.CONSUMER_ID_2 
    AND cal.SENDER_CONSUMER_ID=scs.CONSUMER_ID_1 
    OR cr.CONSUMER_ID=scs.CONSUMER_ID_1 
    AND cal.SENDER_CONSUMER_ID=scs.CONSUMER_ID_2