So I was kicking this around. Very rough first attempt, but it works. I combined your player and maker in a Win Form. You can load the source images by clicking the 'Add' button or dragging and dropping in the listbox. Items can be rearranged by dragging and dropping within the listbox or selecting an item and using the 'up' or 'down' buttons. The out file can be set in the SEQ name box at the bottom. When you have the files added and an out name set, just click the 'Make SEQ' button.
You can view the resulting SEQ file by selecting it from the open button on the tool bar and clicking the play button.
What need to be done is to adjust Kawa's code to allow for using a different order and possibly unnumbered input names. For now it will just use the same location of the in files for the output folder, but this should be by the path passed from Companion, possibly in a "SEQ" sub folder, since this is where Sierra usually placed them. The player controls were just pasted in from another project of mine. I will probably delete the volume slider, but I am kicking around the idea of having it play the aud and or snd resource(s) that would be used in game to be able to check audio sync. This might be more trouble than it is worth.
If there is any interest in this I can put it up on my Bitbucket account after I get it cleaned up and a little more tested.