The IIS URL Rewrite Module 2.1 for IIS7+ may be your friend. The module can be downloaded from IIS URL Rewrite. Using the URL Rewrite Module and URL Rewrite Module 2.0 Configuration Reference explain how to use the module.
Once the module is installed, you can create a host wide redirect using IIS Manager. Select URL Rewrite, Add Rule(s)..., and Blank rule.
Name:
Redirect to HTTPS
Match URL
Requested URL: Matches the Pattern
Using: Wildcards
Pattern: *
Ignore case: Checked
Conditions
Logical grouping: Match Any
Condition input: {HTTPS}
Check if input string: Matches the Pattern
Pattern: OFF
Ignore case: Checked
Track capture groups across conditions: Not checked
Server Variables
Leave blank.
Action
Action type: Redirect
Redirect URL: https://{HTTP_HOST}{REQUEST_URI}
Append query string: Not checked
Redirect type: Permanent (301)
Apply the rule and run IISReset (or click Restart in the IIS Manager)
Alternatively, after installing the module you could modify the applicationHost.config file as follows:
<system.webServer>
<rewrite>
<globalRules>
<rule name="Redirect to HTTPS" enabled="true" patternSyntax="Wildcard" stopProcessing="true">
<match url="*" ignoreCase="true" negate="false" />
<conditions logicalGrouping="MatchAny" trackAllCaptures="false">
<add input="{HTTPS}" ignoreCase="true" matchType="Pattern" negate="false" pattern="OFF" />
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}{REQUEST_URI}" appendQueryString="false" redirectType="Permanent" />
</rule>
</globalRules>
</rewrite>
</system.webServer>