If you are going to use a radio button format with a value list, you have to set up a field for this purpose. That could be a field with global storage--the closest you can come to how this is done in other systems that let you put a control like this on a form without linking it to a table.
You can also create a series of buttons that look and act like radio buttons, but which assign a value to a global variable. Whether this works for what you want to do or not depends on how you design your solution. Data in a global variable could be used to set up a find to find records, but can't be used as a match field in a relationship, for example.