It's supported in the underlying schema, so you should be able to specify it as an element of an SFTP binding.

https://github.com/jboss-switchyard/components/blob/master/common/camel/src/main/resources/org/switchyard/component/camel/common/model/v1/camel-common-v1.xsd#L84

I did notice this is not exposed in the primary or advanced tabs of the SFTP binding in our tooling.  Can you try editing the switchyard.xml directly and adding it?

JIRA to track the tooling bug:

[#SWITCHYARD-1714] FTP, SFTP, FTPS binding pages missing maxMessagesPerPoll - JBoss Issue Tracker

That's interesting, I'm able to add it to the camel-ftp quickstart without any issues.  In any case, Brian has updated the FTP binding wizard to include this value so there shouldn't be any more messing with the XML config directly.  For reference, here's the updated quickstart config with the element:

<ftp:binding.ftp xmlns:ftp="urn:switchyard-component-camel-ftp:config:1.0">
     <ftp:directory>.</ftp:directory>
     <ftp:host>localhost</ftp:host>
     <ftp:port>2222</ftp:port>
     <ftp:username>camel</ftp:username>
     <ftp:password>isMyFriend</ftp:password>        
     <ftp:consume>
          <ftp:maxMessagesPerPoll>1</ftp:maxMessagesPerPoll>
          <ftp:initialDelay>50</ftp:initialDelay>
          <ftp:delay>50</ftp:delay>
     </ftp:consume>
</ftp:binding.ftp>