I suggest a many pronged attack on that front..
1) You somehow convince her it was her idea. Either seeding it and nurturing it until she suggests it, or leave magazines showing houses with them in it and let her develop the image in her own mind before bring it up over wine. A good time to approach this is when sleep is about to overtake her, or when she first wakes up. I find that a very useful tatic
2) You purchase her something very nice for her only, diamonds and gold work well, then give it a few weeks and mention your interest and hope she feels like being fair.
3) You purchase and set it up while she is away and play dumb when she gets home and asks how did that get in the house. Gee honey.. the tank fairy must have came by.
4) Plead... beg and debase yourself until she feels pity on you and gives you her approval.
5) If all else fails, tell her you will give up football on sundays and spend quality time with her at the mall or those plays/musicals she adores and you dread. It's still baseball season, so she will probably forget that promise by pre-season.
6) Dose her with Chocolate and Kisses and hope her brain goes into meltdown, then causually bring it up.
Good luck Mr Phelps... this message will self-destruct in 30 seconds.