Thanks to a wonderful poster going by the name of droptopMBP in the Apple forums, dialing those pesky numbers is now easy with a small amount of up front work. In the notes field for your conference call event in your calendar, simply add a tel URL in the following format:
Note the p for a pause. The only shortcoming of this little shortcut is the inability to add a # at the end, but hey, one button instead of memorizing 9, I like it. The only problem I had is the need to wait a few seconds (like 5-10) for it to finish dialing the access code before I hit the # key. If you listen very carefully, you can hear it mashing the DTMF tones long and slow.
Here is a copy of the exact post with links to details on formatting the string properly:
1) Place the phone string in the "Notes" field (doesn't work in event title or location fields)
2) Prepend the phonestring with the HTML telephone URL "tel://" (ref: https://developer.apple.com/iphone/library/featuredarticles/iPhoneURLScheme_Reference/Articles/PhoneLinks.html )
3) Follow the remaining rules for embedding telephone URLS which you can read here: ( http://www.ietf.org/rfc/rfc2806.txt )
4) Use "p" in place of "," for Pause
5) Don't include "#" (haven't identified a substitute yet
Example: The following works to dial the number 555-555-6543, pause 1 second, then dial the passcode string 123456. You would need to press # on your phone keypad to end the passcode unless the conference service you're using automatically accepts the code after a timeout...
Now, go forth and conference without driving off the road.