I ran into this issue a few months ago and went to the lengths of the earth with Marketo support and couldn't hack it. I wanted to capture any URL parameters if they existed, anytime anyone hit the site. I discovered that Marketo can look for specific URL parameters, like "UTM_region=US" and put the "US" in a field you've created for "UTM_region", but it couldn't return the value of the UTM parameter if you gave them what URL parameter to look for, at least not out of the box. For example, it won't be able to capture the "US" field if you told it to look for "UTM_region". So you'd have to create a set of logic for every possible value for each one of these fields. If you're not using a lot of values, that could be possible, but if you want to get to the keyword combinations, this becomes unrealistic.
It was frustrating, but I'm still looking for a solution. Just thought I'd share.