When you make a RetrieveRequest where the response indicates there are further pages of results that may be retrieved, you'll receive an OverallStatus of "MoreDataAvailable" similar to this response:
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" ...
It isn't currently possible if you just rely solely on the SOAP API. As from Mark's answer, you can perform a SOQL query on User to get the FullPhotoUrl.
But then you are stuck. If the user has a photo defined the URL will include the photo ID starting with the 729 keyprefix. However, Photo isn't currently exposed via the SOAP API. So you can't retrieve it.
You can use good old package.xml and ANT for deploying bulk of components (custom placeholder fields in your case) through a single deployment command. All the custom fields should be listed in the package.xml. Refer to this, this & this to explore this option. You can find many blogs and article related to this on the web.
If you want to stick with VS ...
There is a hidden field _CustomObjectKey which is used in AmpScript, this field may also be requested for DataExtensionObject:
Thanks to Jonas Lamberty for a hint!