There's multiple routes you can go with this. You could have some luck as is with some higher AO-51 or even AO-27 passes, especially if AO-51 happens to be in high power mode at the time. A quarter wave is usually what is used for working the sats in a mobile, since its radiation pattern isn't focused all towards the horizon like a collinear or a 5/8 wave. Quarter waves can pick up from much higher angles.
Another option would be to build or buy a 5+ element 70cm yagi. Arrow antennas are 7 elements, that's what I use and it works great, but 5 is better than nothing. You can use your 2m whip antenna for the uplink and the 70cm yagi for the downlink. I've seen many people go this route as they can sit in the car and easily point the 70cm yagi out the window. It's easier to stick a 70cm yagi out the window than one that has 3 elements on 2 meters on it as well (too big!). If you only have the VX-7R, to use two different antennas on the same radio at the same time, you'll have to build or buy a diplexer.
An Arrow antenna can be bought or a clone built. It's a handheld yagi for both 2m and 70cm. Again since this antenna has two feeds, you'll need a diplexer to make it work with just the VX-7R. If you can get your hands on a monoband 2m or 70cm radio, you can eliminate the need for a diplexer, plus you can operate full duplex which is quite helpful in seeing how you're making it into the sat. It helps fine tune your pointing.
A decent HT antenna isn't entirely out of the question either. I've posted before about the AL800. It's good for working passes about 10 degrees or better and can work all 3 FM sats. Not as good as having some sort of directional antenna, but you don't need the diplexer and you can take it anywhere.
Hope this helps. Let me know what route your interested in going, and I can provide more information, links, etc if needed.
73!
