I'd use either Rebecca Sutterby's or kakeladi's WASC recipe using white cake mix and margarita/lime extract:
http://cakecentral.com/recipes/2322/white-almond-sour-cream-cake-wasc
http://cakecentral.com/recipes/7445/the-original-wasc-cake-recipe
Lime extract is available at:
https://www.lorannoils.com/c-6-super-strength-flavors-candy-oils.aspx
http://www.nationalflavors.com/bakedgoods.htm#baking
HTH
Try this one from macsmom.
Margarita - MacsMom
2 white cake mixes
2 c sugar
2 c flour
1 1/2 t salt
1 pkg cheesecake pudding mix. *Maybe lemon?
10 oz thawed frozen margarita concentrate
2 c sour cream
1 c water
2/3 c tequila
1 T Princess emulsion (or vanilla)
8 egg whites
1/4 c oil
*Lime curd filling
Man, that Macsmom cake does sound good!! Mattie1, you must be a very nice lady because you have the same name as my grandmother and your birthday is just a few days after hers. 
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