At this time, it's not directly possible. But there are a few workarounds:
- Drag and drop selected photos directly from your Aperture/iPhoto library to the Picturelife "Upload or Choose Folders". If you do this, make sure Aperture/iPhoto library is NOT selected in the desktop app Preferences Folders list, otherwise Picturelife will grab your entire Aperture/iPhoto library.
- Select Aperture/iPhoto library in the Preferences Folders list. Once the upload starts, click the Picturelife desktop app drop down menu > select "Pause Upload". From here, open Preferences > Account > Show Local Library. Under the Uploading tab, you'll see thumbnails representing all of the photos queued for upload. Find and select unwanted photos, then click "ignore selected items". Once you've finished ignoring photos, select "resume upload" from the drop down menu.