Wet vents have some pretty specific rules and that would not meet UPC code for a couple of reasons (you could be under a code with different rules that allows this. This difference in rules is one of the reasons that makes it tough to give advise remotely).
However, you mention that there is a another 2" vent after the shower tie in. If this is actually a vent (since this is new contruction and this vent doesn't seem to be serving anything, I am curious why it is there and if it is actually a vent), you can most likely use this to vent your tub. Keep in mind trap arm length maximums.
If you are doing this plumbing yourself, it may be in your best interest to call a plumber for some consultation. We see everything out there in the real working world (which can be very different from the world code is based on) and can usually find a solution for most problems and still meet code requirements.