You do not have many options with regard to DNS zone design for the yahoo.com zone. Your real only option is to point to DNS servers that will provide the quickest resolution for queries. If your current provider is not providing a good service, you may want to try some public DNS servers such as Google (126.96.36.199), or OpenDNS.
Normally, if you had access to the zones, you could load a secondary zone at your location. This is a typical example of a situation where an organization has a central site with remote sites at different locations. In this typical scenario, the DNS administrator may implement secondary zones at the remote locations so that each remote location has a local copy of the DNS zone. This is not possible with the Yahoo.com zone, unless you can convience them to provide you with access. It is customary to lock down the zones you own and NOT allow untrusted orgnazations/individuals to have access to your zones.
The alternative (NOT RECOMMENDED) is for you to create your own copy of a DNS zone called "yahoo.com" at your location and then you create all of the records and point them to the correct IPs. However, this design is not recommended because of the following:
You would have no idea when a host changes its IP address. Name resolution will stop functioning for you when this happens.
You most likely will not have any idea of all of the records you would need to create. I am confident that yahoo has many, many records in their zone.
Since your local copy of the zone is authoritative (your DNS owns and hosts it) any record you are missing or incorrect, will cause name resolution to fail for those records in the yahoo.com zone.
In summary, my suggestion is that you try to improve your connection to the internet, and use DNS servers that are highly available and provide fast response.