If you're willing to risk significant damage to the Nexstar, and possibly hurting someone if it gets out of control, go for it!
Sorry, let me start over. Since you've built up additional experience, your time to solo the Nexstar should now be shorter. Rather than risking a more expensive plane, and potentially hurting someone, give your instructor a call. Tell him you've been practicing with foamies and that you think it's helped you progress. Explain that you are anxious to solo and see if you can work out a schedule. If you can't match schedules, ask if there might be another instructor whose schedule might be more in line with yours. I can't speak for him, but I know I wouldn't have a problem with such a call.