Here's a device driver that can be used for setting a variety of values (text, number) which can then be used in SharpTools.io dashboards.
To use it with Hubitat's Rule Machine global variables, you could create a triggered rule which watches for your desired variable to change and then copies the value from the variable into one of the devices supported commands.
For example, in the following Rule, I'm watching for the MyText global variable to change and then using the Notify capability of the Virtual Values device to set the text attribute.
And here it is in action directly from the device:
