Other than comma, are there any supported pause characters in a dialing string? On a Blackberry, a phone contact with the form:

1-800-555-1212 x1234#12#7#123456
1-800-555-1212 ext1234#12#7#123456
1-800-555-1212,,,1234#12#7#123456

all worked.

On my Android (Samsung Galaxy S5 with 4.4 Kitkat) the shortcut x, and ext do not work. You are supposed to use a comma (actually three). 

However, Outlook (in Office2010 at least) will not let you save a contact as:
1-800-555-1212,,,1234#12#7#123456

It insists on inserting a space before the commas.  But Android sees the space as end of phone number processing. Interestingly, it lets you enter this in a Meeting location, or as a string in an email, and Android will process this properly.

Are there any alternate pause characters I could try, so as to get around this Outlook limitation?
Have you tried  "P"  for pause gives a timed pause on remote phone and at least some other phones.   Use more than one if you need additional pause time.