Just import the private key into the bitcoin client
do this for every private key and it will all end up in the same wallet.dat
there are lots of tutorial on how to import a private key, and it varies between bitcoin clients
eg
Run Import Command in Debug Window
In the console at the very bottom is a text entry box. In here enter:
importprivkey yourPrivateKeyInWalletImportFormat "TheLabelThatIWant"
then wait a while - it takes a few minutes to complete
https://en.bitcoin.it/wiki/How_to_import_private_keys_v7%2B
do this for every private key and it will all end up in the same wallet.dat
there are lots of tutorial on how to import a private key, and it varies between bitcoin clients
eg
Run Import Command in Debug Window
In the console at the very bottom is a text entry box. In here enter:
importprivkey yourPrivateKeyInWalletImportFormat "TheLabelThatIWant"
then wait a while - it takes a few minutes to complete
https://en.bitcoin.it/wiki/How_to_import_private_keys_v7%2B
http://translate.google.com.hk/?hl=zh-CN&sl=en&tl=zh-CN#zh-CN/en/%E8%B0%A2%E8%B0%A2%EF%BC%8C%E8%BF%98%E6%9C%89%E6%B2%A1%E6%9C%89%E5%85%B6%E4%BB%96%E7%9A%84%E6%96%B9%E6%B3%95
There doesn't need to be another way. This way works.
It can be a bit slow, but you just have to be patient.