After experimenting some more, I found out how to get the bracketed numbers for the IEEE style right aligned in the Bibliography. If anyone else wants to do this, here are the steps. There are about 2 dozen steps, but it is pretty straightforward. You first need to add a new citation style for IEEE to Zotero, then you need to modify the Bibliography style in Word.

1. Open https://editor.citationstyles.org/searchByName/ and find IEEE and click the Edit button.
2. When the Visual Editor opens, choose Bibliography in the left pane, and click on Layout below it, and then click on "citation number (variable)" below Layout.
3. In the main window on the right, find the Affixes section.
4. In the prefix box, replace the [ character with 	[
5. Next, click on Info at the top in the left pane.
6. In the main window at the right, find the Info section.
7. In the Title box replace IEEE with IEEE-tab. This gives this Zotero style a name different than IEEE so that you don't overwrite the original IEEE style.
8. In the ID box replace http://www.zotero.org/styles/ieee with http://www.zotero.org/styles/ieee-tab
9. Find the Links section. It's located below the Info section in the same window.
10. In the first box under the href column and left of the box that contains "self", replace http://www.zotero.org/styles/ieee with http://www.zotero.org/styles/ieee-tab
11. Now, you can save this new style to your computer by clicking on the Style dropdown located on the left side on the menu bar, and choose Save Style.
12. A dialog box will open. Click the Download button to save the style to your computer. If you are using Windows, the file will probably be saved in your Downloads folder.

Next, you need to install the csl file in Zotero.
1. With Zotero open, click Edit > Preferences.
2. When the Zotero Preferences dialog box opens, click on the Cite icon at the top and click the Styles tab below it.
3. Click on the + button.
4. Choose the csl file you downloaded, and click the Open button. The "IEEE-tab" style will now appear in the Style Manager list.

Now, you need to tell Word to use the new citation style. Make sure Zotero is still running.
1. With Word open, click on Zotero on the main menu. This appeared on the menu when you downloaded and installed the Zotero plug-in for Word.
2. Click on Document Preferences.
3. When the dialog box opens, choose "IEEE-tab" in the list of Citation Styles. Then, click OK.

Finally, you need to modify the Bibliography style in Word to use the new IEEE-tab style.
1. Find the Bibliography style in Word and right click on it and choose Modify. (If it's not located in your Styles Gallery, Google will tell you where it is located, and how to modify it.)
2. When the Bibliography Style dialog box opens, click the Format button at the bottom, and choose Tabs.
3. When the Tab dialog box opens, clear any tab stops, and add one tab stop at 0.3 inch, and be SURE to select the Right alignment radio button! Next create another tab stop at 0.4 inch making this one Left aligned. Then, click OK to close the dialog box.
4. Click on the Format button again, but this time choose Paragraph.
5. Under the Paragraph setting, in the Indentation section, set Special to "Hanging" at 0.4 inch. This number should match the number of the second tab stop. Use 0.5 inch if you want more space between the bracketed number and the beginning the text.
Note: You may need to adjust the numbers for tab and indent depending on the font you are using in your Bibliography.

That's it. Now, select the entries in your Bibliography, and click Refresh under Zotero, and your bracketed numbers will be right aligned.

If you are using a citation style different than IEEE that numbers the entries in the bibliography, the steps to right align the numbers are probably very similar.