Way to buy out a share of a friend's house, not the whole thing

[Ben G.]

I have a friend who just got a fantastic deal on a new property. The house she lives in was a good deal too, but she was looking to upsize and the new property bid was accepted at ~66% of what she thinks it will eventually appraise for. I'm trying to convince her to keep the first home and rent it out rather than selling it, as she makes good money and can keep going without pulling out the equity. If she wants at least some equity out, is there anyway that I can legally buy in on the property without selling the property? Is the only legal way for this to happen a sale to me or a sale to a shared entity (i.e. LLC or partnership)? Does that immediately trigger a due on sale clause or is there a way to legally help her get some equity out of the home without losing the property as an investment, having to find a fresh mortgage or pay taxes on the full value of the home (i.e. perhaps only pay taxes on the 1/8 or 1/10 share that I buy out).

I'm looking for a way to convert this from a one time good deal for a friend into a better, long term income producing deal for both of us.