Hi,
If you own both the sites you can just do a 2 way link exchange if they are in the same niche, if they are related sites and you both own them I do not think it is such a bad thing.
I mean if you are really worried about factors around Google placing value on these links then you need to think of all the possible factors in which Google can see networks of websites:
-
Is Google look at my analytics CID codes on websites I own, an easy way to spot networks?
-
Is Google looking at Whois data?
-
Are you running Adsense on all these sites with the same publisher ID code?
In the end the best type of link building is not using your own websites it is going out into the market and looking for quality link opportunities, making great content and syndicating it to related sites, the list goes on really it is endless what you can do.