This is possible. We are doing the same thing in the company I work in.
We put .ipa and .plist file on the server and provide link to .plist file. When user clicks on the link from their mobile device they are prompted to install application.
The only necessary thing is to include UDIDs of all devices to the provisioning profile with which you are signing your application.
This is the content of the .plist file:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>items</key>
<array>
<dict>
<key>assets</key>
<array>
<dict>
<key>kind</key>
<string>software-package</string>
<key>url</key>
<string>http://location of your .ipa file</string>
</dict>
</array>
<key>metadata</key>
<dict>
<key>bundle-identifier</key>
<string>your.app.identifier</string>
<key>bundle-version</key>
<string>3.5.2</string>
<key>kind</key>
<string>software</string>
<key>title</key>
<string>app_title</string>
</dict>
</dict>
</array>
</dict>
</plist>
And then add link to your plist file:
<a href="itms-services://?action=download-manifest&url=http://location-of-plist.plist">
Download application</a>