If you have not formally left the Catholic Church, then you are bound by Catholic marital law. Your marriage to a non-Catholic in a non-Catholic ritual will not be recognized as valid by the Catholic Church unless you receive the appropriate dispensations from your bishop. What’s been recommended to you is that you marry invalidly in a civil ceremony and then try to fix the situation by finding a priest to “bless” your invalid marriage. As I hope you can now see, a faithful Catholic priest is not going to “bless” an invalid marriage. What would have to happen at that point is indeed a convalidation (i.e., validating an invalid marriage).
I also hope that you do not think so little of your upcoming marriage that you would deliberately marry invalidly and then seek to “fix” the marriage later. What should be done is that you and your fiance should meet with a priest to discuss how you can be married validly according to Catholic marital law. You will need a dispensation from cult to marry a non-Catholic and a dispensation from form to marry in a non-Catholic ritual. If your fiance is not baptized and is strongly opposed to a religious ceremony, a bishop might – and I mean might – allow you to marry in a civil ceremony.
As for your fiance, if he is unwilling to do what needs to be done to marry you validly then you will know just how much he thinks of you and your upcoming marriage.