lots of vit C to bring down inflammation and stimulate collagen production, cell renewal, etc. I'd do so topically and internally.
Skin brush over the areas NEAR marks, to flush lymph and make tissues look cleaner and smoother...gently and never directly over any irritated/red areas.
MSM- Prevents the disordered collagen cross fibering that makes scar tissue feel rigid. You can get a cream cheaply, and if you are really trying to do as much as you can b4 your vacation, you can also take it internally to bring down systemic inflammation so scars appear less "angry" red.
Calendula- Just nice for healing irritation. A friend of mine was suffering from burns and itching post-radiation treatments, and calendula oil from the local herbalist was the ONLY thing that wound up helping.
Also, you can envision clear, glowing skin over the area, and thank your body for stretching to afford your baby room to grow and be born, while releasing it from any need to carry scars (which is what stretch marks are), be they inner or outer, from the circumstances of that birth. MAke sure to focus mostly on the imagery of healthy, beautiful skin there as you want it to be most of all. Then imagine a beautiful light of healing washing over the area, smoothing every inch of skin it touches, like a warm, magical laser-eraser. I healed a gouge in my hand that went more than 1/4 inch deep this way while less severe cuts on my hand- from the same accident- scarred and became raised and discolored for the next year. The gouge, which was the worst of all my boo-boos, healed twice as fast and looks like perfectly normal skin. Go figure, eh?
Good luck, and remember that even if they are visible, stretch marks are a beautiful sign that your body has created a beautiful human being- a marvelous accomplishment!