The easiest method (if you don't change passwords much, which if you use Keepass you probably do) is to duplicate the database using the 2.x version.
There isn't too much of another way. If you actually look at what's going on with the encryption, you'll see that if it encrypts the whole thing with one key, it can't decrypt it with another because that's the very point of encryption.
If you tried to use more than one key, in any way, it would be reduced to verifying the key and then using a stored key unlock the database, which is quite insecure.
Even if the program stored two copies with two different encryption keys in the same file, that both makes it easier to brute-force since getting one key makes it easy to find the other key, and clumsy because every time you edit the passwords you have to have the other key.
Tl;dr: having multiple keys possible but with only one needed is almost mathematically impossible.
One other solution you have is to get a shorter password. Reading this article, concerning AES (which is what Keepass uses), a password as simple as
fluffy is puffy would take maybe 39 miillion years to crack even though those words are very simple.
By comparison then, Keepass hashes the password 6,000 times by default (and if you set it to 2 million it would still barely break a sweat) which makes any sort of mathematical trickery useless. You can use the pronouncable and lower+upper+num settings on passwd.me to generate a password that's easy to learn and remember but hard to brute force or guess, like
tahter.3usandu. Heck, you might even end up learning Japanese :-).