How to Show Passion

I'm guessing you're a high C and you're probably in a high I environment.
I'm a high I, and while 'passionate' is not an adjective I would use to describe myself, others have described me as such. I've worked in a high C company and once I realized I was not 'with my people', I had to seriously reign it in to fit in and stop looking like total weirdo. Ultimately, I was not very happy there and left before long.
But when someone first described me as 'passionate', I was surprised and asked for specific examples of why they thought that.
They told me I spoke emphatically in meetings, defended my ideas, was very animated, asked lots of questions, and just generally used 'bright' adjectives (ex. cool, interesting, novel, awesome) to describe things I learned or others' ideas. (All of which are hallmarks of the 'high I'.)
(Also, in this particular context, I was working for a major airline and thought it was just about the most awesome job in the world, so maybe it came through more naturally : )
I'm sorry that this is not a direct answer to your question, but its sort of a corollary story as food for thought.
-Alex

 I am a high d high I and work with a lot of high c's.  Once in a discussion a colleague of mine asked me:  "why are you angry?". To which I replied I wasn't angry and he asked: "then why are you talking so loud?". Since then I like to believe I have lower my tone of voice, it takes a lot of effort though, a conscious effort.  It drags a lot of energy away being someone we are not.  I guess what we high I's do naturally that convey passion are:
1 - we smile me lot
2 - we talk faster, making a lot of gestures, way outside our body limits
3 - we talk about ideas, almost as if we could touch them, see them, almost as the ideas were already a reality
4 - we make a lot of future projections, not at all considering something could go wrong, we don't worry about the details of how we will achieve the results we plan, we just have this natural belief we will get there
I am not sure if that helps, my recommendation to you is to think: "let's see, what would a high I think in this situation, concentrate on that thinking, make it your own and I think your own actions will reflect a bit more those of a high I and convey passion the way a high I naturally does it.  At least this is what I do when I want to tone down my high I characteristics: "how would a high c behave here, and I start thinking about the risks, the plan, and when I am in that mind set I immediately think twice before I say anything, which is for example, one behavior I make an effort to change - talk less.
The other option I guess you have is to transmit with words what you cannot convey as easily with your gestures and tone of voice.  State that you are excited about the position, or something else, and explain the reasons of why that is so, and make a projection in the future of the results of that action.  Say for example your wife invites you for dinner, you show no excitement, she draws the conclusion you don't really care whether you go or not.  To avoid that but still be yourself you can say something like: "I am looking forward to our dinner tonight, we haven't been out for a while and I have heard thi restaurant has very good food and ambience. We will have a very good time.". I know just to say that is also an effort for a high c, but it is probably a lot easier than conveying passion through your actions and it will have a positive effect.
Nara