Not within a default installation, but you might take a look at some of the one-page checkout extensions -- I think
Uber Checkout can list payment methods as dropdowns, although I believe it does all the options, not just individual ones.
If you can't find one that works for you, you'll probably need to hire a developer to create a custom modification for you. If you need to find one, I recommend you post a request in the OpenCart "Commercial Support" forum (forum.opencart.com/viewforum.php?f=88), which is checked by a number of OpenCart developers. You can also try checking out the OpenCart "Partners" area (
www.opencart.com/index.php?route=partner/partner).
