Transparent (Blank) BaseMap(tiled) URL(map server)

My iPad app released 1-2 dos back, where by mistake I added Base Map layer which should not be case for some of our clients. Base map URL I get from a database, so my question is, is there any transparent Base MAP/ Tiled MAP URL I can use? (I cannot change code by making opacity 0 or anything, as I need quick fix, if I go about changing code I will have to seek app approval, which will take another 10 days). Please do help me out if anything is available. At present they can see base map layer. I wanted URL of base map which act like transparent layer like by default Opacity 0, something I just have to add to client database which will be transparent making base map invisible, so that client will not be able to see base map.