You can do the basic copy and paste of script method to blogspot.com but the key is you'll need to change from HTTPS to HTTP within your Subscribers dashboard which is a bit weird but that basically enables that method for the installation.
This is an easy change though. Just make sure you're logged into Subscribers and.scroll down under SITE DETAILS then change your "SITE URL" to HTTP
This little dropdown is what you need to toggle to HTTP: (NOT HTTPS)
Now, please scroll down on your account dashboard and navigate to "CODE INSTALL"> under Manual installation, you'll find your installation code to paste to your website admin.
Now go to your Blogspot admin back end and click Theme in the left side menu.
Then click Edit HTML under your template.
Insert your Hello Bar code before the closing </body> tag and click Save Template.
Please note that our system may recognize some errors with the installation but once you confirm that the installation is done correctly, you may click on the "Override verification" regardless of what error messages are showing.
Lastly, please note that with this installation method which required switching from https to http within the Subscribers dashboard, the browser-native pop-up will not be available so you'll only have the Custom Prompt (Chicklet) similar to this one below.
You can go to your Dashboard's settings>Prompt settings page to further customize your opt-in prompt.
I hope that helps, please let me know if you have further concerns.