Although very much a newbie to FM, I would think that you could script it from the field that hosts the dropdown list.
Make a script with a bunch of If functions to run OnObjectModify on that field to direct the user to the layout you want. Then, when they select an item from the list the script should run and take them there.
I just tried it on an old file and it seems to work.
OnObjectModify requires FileMaker 10 or later, just to clarify.
Your script doesn't need any "If" statements, you can simply tell it to go to a layout by calculation, and in the calculation specify the field with the drop-down list of layout names.
Or, with FMPA, create custom menus for navigation.
I did it this way (with help from experts on this forum):
1) Name your layouts the same as the choices in the pull down list/pop up menu.(or make the choices match the names of the layouts)
2) Write this script:
Set Variable[$Layout; Value:Table_Name::Name_of_FIELD_with_the_value_list]
Go to Layout [$Layout]
3) Attach the script to the field with the value list using an OnObjectModify script trigger.
There are probably slicker ways to giterdone, but it worked for me...
And this is asuming you are using at least FMPver10
onobject modify worked perfectly