This is a great question. Thanks for posting it on the forum!
You have a few options to do this:
1. Fake it with another text object
2. Use the Advanced > Text > join block
3. Use a Number Input instead of a text block. The Number Input can be configured to use a prefix, and can be made "read only" - both in the properties panel. I'd recommend this because it gives you the most control over the decimals.
Here's how to do these - https://www.screencast.com/t/QleiREqTN2
Hope that helps!