No, you just need to block it off incrementally. Go in 4 blocks, build a 2x2 dirt "wall" there, then come back out. Then fill in from 3 blocks in, 2 blocks in and 1 block in. Then remove all the dirt blocks. Water will come in from the 5th block out, but it wont create any source water blocks. Push past the current of water and go in another 4 blocks and repeat the pattern until that section is clear of blocks. Keep repeating until you reach the other side of the tunnel. It's a boring process and the current will always be against you, but it's doable. With a tunnel that size, it should only be about 10 minutes.