Both flaked corn and flaked barley need to be mashed with a malt with a high enough diastatic power to convert the starch to sugar. If you use them in an extract batch then all you'll get out of them is a starchy haze. As far as I know, there is no alternative. What recipe are you trying to convert?
Can you do a partial mash? ie. mix together 2-3 lbs of grains in a mesh bag and hold them at 145-150* for 30-60 minutes? If that is possible for you, then you can mash the corn +/or barley with malted barley and get all the benefits of a full AG mash.
Please tell us why you cannot do all grain. It really can be nearly as easy as extract. I use the pot that I had used for extract (5 gallons) and a paint strainer bag to do 2 1/2 gallon batches all grain (BIAB). If you can measure water, heat water to 160F, and have a coat to insulate the pot, you can do all grain.
Even a partial mash will provide mashed base malt for conversion. Here is a well-written primer on partial mash brewing. All you need is your existing gear and a mesh bag to hold the grains. You can buy paint strainer bags at any home center store for a few bucks.