Asking a colleague for his submitted paper A colleague just told me about a paper he submitted to a conference, I'd love to have a look at his work out of curiosity. 

How can I ask without him thinking I'm off to steal his ideas or something?
If he is a colleague, he is unlikely to think that. Just express your interest and ask for an early look. If something in it seems interesting to you contact him again and see if you have the possibility of collaboration on an extension or similar work. 

It is how collaborative relationships get formed. Just do it.