You are so cute. You remind me of a younger and nicer me. =)
To start, I would suggest that you do not stand up before the curtain call. That's mainly because you are blocking someone else's view. Even if it's brief, it's not the most polite thing to. Unless it's like what antiandrewx said, and the whole audience is on their feet.
I have not been blessed thus far in seeing a performance so powerful that I was tempted to get out of my seat before the curtain call. But I have vocalized my appreciation after a few special numbers (no words, but I WILL 'whoop' if the spirit moves me). I've done this a few times. Once during one of Julia's solos in 'Wicked', once during Frenchie's 'Seasons of Love' solo, and once during dance performance at City Center. Now all of these shows are more lively that other shows that I've seen and the audience was very into it from the beginning. They were very vocal, and so I was totally in line with them. I tend to refrain from whooping and such when they subject matter is serious, but that's just me. People whooped when I saw Les Miserables, and I didn't think it was tacky. It's just not me.
Now, when the curtain call comes up, if I want to stand, I stand up ASAP. I'm not really worried if I'm alone or one of a few doing it. I don't "stage door", so my only way to express my gratitude for an excellent show is to stand and be seen my the cast. I can't think of any actor who would not appreciate people who gave them a standing ovation, even if that person was one of of 4 or 5 people. Love is love, and everyone likes to feel it.
"I'm-Not-That-Boring-Low-Ass-Girl?! You better go up at the end!" - Seth Rudetsky to Julia Murney about her Solo CD choice