Your workflow presents an interesting use case and I can see the value in targeting the creation of your missions. Pix4Dcapture does not natively support spontaneously creating a new mission that is centered on your drone’s current location while it is flying a mission.
If you want to fly with Pix4Dcapture I recommend enabling Pix4Dcapture’s Advanced Mode so that you can plan your preliminary survey mission with the lowest amount of image overlap that will allow you to visually identify points of interest. Download your images to a laptop and plot the X, Y, Z position of each image based on its geotag in a GIS software that can export vector files as a KML. Scroll through your images to identify the presence of a point of interest and then identify the location of the image in the GIS software.
If you expect your flight plans to always be the same size you can save time by creating an automated process that generates a KML polygon that is centered on the X, Y position of the image in which you identified the feature of interest. If each mission will be different, simply digitize an approximate boundary of the area you would like to fly with your targeted mission. Export the KML boundary to Pix4Dcapture for Android and plan your targeted mission based on the footprint of the proposed mission.
I am unaware of any flight planning software that natively supports your workflow, but someone else in the Community might know. Don’t hesitate to let us know if you have any questions and please consider letting us know what you end up doing to capture your images.