If you can name a set of trust anchors (e.g., with an environment variable, in a configuration parameter, in a command-line argument, as a function/method param

If you can name a set of trust anchors (e.g., with an environment variable, in a configuration parameter, in a command-line argument, as a function/method parameter), then you've got the power to specify what to trust contextually. The problem is that a) apps usually don't give you such a control, and b) the names of these sets of trust anchors have to be meaningful to users. (b) is a pretty tough problem!