When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Since you included the "other than removing both dash sides", the answer is "Yes". The right side is pretty easy and will show you what you have to do on the left.
Nothing is easy on a C3. If I remember correctly, you first have to remove the driver side A-pillar pad. Then you you will have to carefully bend the dash pad to get it to slide up the A-pillar so that the driver side speaker is up high enough to disconnect the speaker from the pad. The real problem is that your dash pad may be so brittle that it will crack when you try to pry it up and gain space from the top of the instrument cluster and the underside of the pad.
It was quite a long time ago when I replaced the speakers. I can't remember for sure but I may have had to drop the steering column and loosen the instrument cluster so that it would drop with the steering column in order to gain clearance to reach the nuts the attach the driver side speaker to the instrument pad.
The passenger speaker is fairly easy to reach without moving the dash pad.
I know that some people have suggested warming the dash pad by leaving the car in sun. Or even using a hair dryer to warm the pad if you are stuck in a garage.
I know that I replaced both speakers in my 75 vert. When I got done, I was quite sure that St. Louis probable installed the dash pad before they installed the windshield.