Add button next to a field that forms an URL and opens webpage.

Need to add a button on the accounts page next to a new text field.  Something similar to the web field in the communications options:

I need to be able to enter a text value like: “asd234” into the field to be stored as an “external account id”. 

Then be able to click the button at the end to display a webpage in another tab with an url like:

https://somewebsite.com/asd234

I was planning on using a System Setting to store the URL root https://somewebsite.com/ and then just append the “external account id” field.

I envision the button click code to be something like (pseudo code):

If (account.externalaccountid <> '') {
	Var URL = get-system-setting(“external website root”) + 
              account.externalaccountid;
	DisplayWebPage(URL);
}

NOTE: the functionality of the Web field is what I want except that I need it in another section under “billing” and need to store just the “external account id” – not the whole URL.