Some options you have are

1) Would be to have a config file that is located in your modules directory that the user can enter global setting used by all instances of you module.

2) Add a section to the web.config file that constains global setting just used by your module.  If you did this option you would need to remember to copy over the settings to new web.config when you upgrade DNN.

3) Create an admin module for you module that all it does is provide a way to set global settings.  This module would write the settings to a table created in the DNN Database to hold the global settings.  Your modules would then get the information from this table then connect to the database in the global settings table.

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#1 & #2 would be the best solution if this is for an personal site and the module will only be used in-house and you have easy access to update either the config or web.config file.

#3 would be a better soltuion if this is a module that you were going to distribute commercially for other people to use.

MJ, interesting solution for his use case.  Just goes to show the ingenuity of members of this community.