You can't pre-fill the auto-suggest list as far as I know. You can try using
the auto-resolution feature. If you enter part of a name or a nickname then
tab out of the field (or hit Alt-K [Check Names]), Outlook will attempt to
resolve the name against your address book. If it can't it'll red underline
it and you can right click on the name to manually resolve it. Outlook will
save the resolution for future use.

There is a third party utility you can use to edit and populate your
autocompletion cache.
http://www.dcs-imaging.com/owtlook.htm

The manufacturers of this software have also provided a (free) method to
populate your autocompletion cache from your existing Contacts. Here it is:
In MS Outlook, go to tools, options, mail setup, send/receive.  Uncheck the
"Send immediately when connected box".  Next, press the Send/Receive Button
(in Options) and uncheck "Schedule an automatic send/receive". Finally,
click "Work Offline, or if you want to be extra careful, disconnect your
computer from the internet by removing your network and/or telephone
connection.
Now open a new e-mail, press the bcc or to or cc button, select the contact
folder you would like to bring into your NK2 (autocomplete) file.  Select
all names by highlighting first and last contact and then add them by
pressing the OK button at the bottom.  With your computer disconnected from
your mail server, press the send button.  This will automatically populate
your autocomplete file with all of the selected e-mail addresses.  Next, go
to your Outbox and delete the e-mail(s) that you just created.  Go back into
your Tools, Options, Mail Setup, Send/Receive and change your options back
to the original settings.   Remember to put your mail settings back and plug
in your removed cables.