well, the only way to have custom sounds, would require the app to be running all the time. it would require the app to say something like: "If You want a custom alert sound, don't close the app, leave it running in the foreground."
the app would then have two very different modes of operation, adding complexity to it.
ii added more than 150 short sounds for the alert sounds as InAppPurchases, to deal with this, but people still ask for custom or recorded sounds. :)
maybe ii should do it and make it a special feature that can be bought as an InAppPurchase. would You buy it if it existed? throw me an email and let me know
currently the alerts are just simple Local Push Notifications, their audio sound is limited to 30 seconds max and has to be included in the application bundle - hardcoded. ii can record it on the fly, but ii can't add the recorded sound to the Notification. if that would be possible ii would naturally done that first. because the alert sounds are just notifications, the app does not need to run in the foreground all the time.
so ii decided to keep this in mind and if ii get more requests for custom alert sounds ii will definitely code it.
ii want the app to stay simple and powerful, ii don't want it to do everything, ii just want it to simply remind me to do a reality check. a custom sound may be more fun, but the default one is already great and does the job very well. ;)
the goal is not to listen to music, the goal is to awaken during a dream and stay there as long as possible. :)