That is not possible. When you suspend a subsription, a rewrite-block is added to httpd.conf:
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{ENV:REDIRECT_STATUS} !=503
RewriteCond %{REQUEST_URI} !\.(jpe?g?|png|gif|ico|css)$ [NC]
RewriteCond %{REQUEST_URI} !robots\.txt$ [NC]
RewriteRule ^ - [L,R=503]
</IfModule>
This leads to the 503 page. But this new block must be loaded into the Apache configuration. That is happening when a graceful or full restart is executed. That reload or restart is executed after the configured server restart interval has expired. For that reason you need to wait a while until the new setting is applied. However, if you reload/restart Apache manually, the setting will be read immediately and applied.
When you do not see a change in your browser it is probably for the reason that a cache is still delivering the previous page content. As you can see, there are some conditions ahead of the rewrite. It is only applied if the file does not end on an image extension and is not robots.txt. This shall ensure that the suspension is search engine friendly.