Thank you for the information and your question. Although I can understand your dilemma, unless you had been issued the plackard or had someone in the vehicle who was entitled to use it, there is no defense to the citation. You could plead your case to the court to get them to lower the fine (the range in the statute is $250-$1000), but you need to keep in mind that you could have, but weren't charged with a misdemeanor
. In other words the officer that ticketed you had a choice, as does the DA to charge you with a criminal charge or to issue a citation/fine which is akin to a parking ticket
. So, although again I understand your situation, this could have been much worse and you still wouldn't have a defense based on the elements to the violation.
If you can convince the court of your medical condition and also show financial hardship they may reduce the fine, but they could (not likely but possible) change the charge to the misdemeanor. Also, just so you are aware, your friend that let you borrow the plackard could also be charged.
If you want to learn more about this statute and the possible charges, penalties, and defenses, there is a good artivle at the following link: http://www.shouselaw.com/disability-placards.html
Please let me know if you need any clarification.