Hostas will fry in a sunny area.

Not necessarily. There are sun tolerant hosta that fare quite well.

Chinese Sunrise, some of the "red" varieties, Jimmy Crack Corn, Maui Buttercups, and some of the darker, thicker leaved ones. Among many others.

The ones with white in them generally fry. If the texture is fine, they'll fry.

For the best results, do it after they bloom and not when the weather is 104F like is here in Maryland. I would do it in the fall when the leaves start to die off. Then they'll have the entire winter to acclimate. You can divide them at the same time, so you could have more to create a really nice border.

Of course, I have no idea what your hosta look like! :)

You don't say where in zone 4 you are, but in my Minnesota zone 4, most of the hostas can take full sun and just about anything approaching full sun. The "blue" ones will lose the coating that makes them blue leaving you with a green plant; and as said above, the variegated ones don't fare as well.

That being said, nice flowers and foliage year around will be a challenge. There are dwarf and mini conifers, of course. But your hosta naturally die back in the fall anyway as will perennials and certainly annuals; deciduous shrubs will lose their leaves. Maybe everything's under a few feet of snow anyway - like it tends to be here most winters.

I'm right between zone 5/6 and hostas do ok in full sun all over town. I am over-run with variegated ones and the green/white contrast isn't as nice in full sun compared to the ones in shade.

A quick count tells me I have 42 hostas (probably forgetting a few) and many could be divided further. Half are in really sunny spots. I like to divide in early spring when the shoots are just showing purple tips because then they leaf out really nice for the whole summer. Along side them I have tons of yellow daylillies and tons of Autumn joy sedum and they like full sun. Lets see, I also have some salvia and coreopsis and some bright pink dianthus all near hostas. I also have tons of purple bearded irises, but they are really boring, in my opinion, once the blooms are gone. I actually have a Jacob's ladder in a pretty sunny spot and it does ok.

But perennial will all die back and you'll have nothing in winter. But I"m guessing in zone 4, you'll be under a blanket of snow anyway?

Also, the burning bush loses it's leaves - not evergreen.