I did this. I started putting money in Vanguard Wellesley Income Fund Investor Shares (VWINX) (40% stocks, 60% bond .22% expense ration) in a taxable account 6 years ago when I decided to start saving for a downpayment. Then I moved it to Vanguard Tax-Managed Balanced Fund Admiral Shares (VTMFX) to reduce the amount of tax that I was paying on dividends. The expense ratio is 0.11%, it is 50% bonds, 50% stocks, and the bonds are invested in tax-free municipal bonds.
I'm still not sure when I'll buy a house. At the earliest, it will be one year from now but most likely it will be another 2 to 3 years away. In the meantime, I'm really glad I chose to invest my downpayment because it has grown at a 7.3% rate of return, which is magnitudes more than if it had stayed in a savings account.
I can't say that this is the best choice of funds but it is the one(s) that I felt comfortable with. Looking back, I didn't realize that it would take me so long to buy a house. The decision was more for personal reasons, not financial. If I had known that it would take me 7 to 9 years to buy a house, I might have chosen a slightly more aggressive allocation. However, I don't have any serious regrets.
Better to invest now and tweak your fund choice later than to sit around trying to choose the best fund. It won't matter that much if you choose to change funds 3 or 4 months from now.