I just fired up my 740, and went to Menu>Check for Updates. iFly shut down and went to the Update screen, and although the only thing available was Weather & TFRs, the bottom of the screen had:
A box to Select/Deselect All, An indication of the number of Items Selected And the Download Size
Below that are four buttons:
Cancel Save Selections Fast Wx/TFR update Install Selected Items
If your 740b is set to download ALL states, plus Wx & TFR's as well as new software updates, you should be able to, at your hangar, "Deselect All", then just check the State(s) you want, and the Weather & TFRs then click on "Install Selected Items". This should download just what you selected, and retain the choice of ALL the states, etc. when you bring the unit home and have the time and ability to download all the additional information.