Width + rotation

I’m using ActionScript to enlarge a movieclip by a percentage of it’s width on each frame. At the same time, the movieclip is rotating. The movieclip is not circular, therefore as it rotates, it’s width changes, and therefore the rate of enlargement also changes. I’d like it to enlarge at a contast rate, how can I do this? I toyed with the idea of placing a circular shape around the outside of my movieclip, but the movieclip is being used to mask an image, and i dont want a circle cut out of my image.

    // make the flower grow in size and rotate
    this.mask["flower"+i].onEnterFrame = function() {
        // increase size
        this._width += ((this._width/100)*2.5);
        this._height = this._width;
        // if the size gets bigger than 1000px wide, stop increasing it's size
        if(this._width > 1000){
            delete this.onEnterFrame;