You know in all the time I have had Sparkle I have come to realise it’s like this… I’m a kid with a large box of blocks that I have piled onto the floor. Creatively I will sit their for hours coming up with anything and everything I want with these blocks - I let my imagination go wild!..
This it the attitude I take with Sparkle and magical things happen! 
@say_whaaat , I have learned to live with the limitations of sparkle and appreciate the areas that it sparkles in ( sorry about the pun ). Recently I inquired about different buttons and better control over the graphic slider and the limits it has for a project. The response was it is on a list and others expressed the need as well.
For my project, I end up using an external source to get around the limitations of the slider to complete my project. This end up in a snipped inside an embedded object. The embed recreates the entire slider without any sparkle code. Maybe you can build out the functionality and have the button inside the snipped and this is an embed.
By the way, my new slider has different arrows and has the ability to have 2 button clicks for each image to offer 2 different options. The sparkle slider is good, but very limited. The other option is to work backwards and look at the source code and add in your code into the existing files. The issues as some other have pointed out is an update will wipe out your manual code. This is a last resort method for me.